Placing and Share Consolidation

THIS ANNOUNCEMENT AND THE INFORMATION CONTAINED HEREIN IS RESTRICTED AND IS NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION, DIRECTLY OR INDIRECTLY, IN WHOLE OR IN PART, IN OR INTO THE UNITED STATES, AUSTRALIA, CANADA, JAPAN, NEW ZEALAND OR THE REPUBLIC OF SOUTH AFRICA OR ANY OTHER JURISDICTION IN WHICH THE SAME WOULD BE UNLAWFUL

THIS ANNOUNCEMENT IS FOR INFORMATION PURPOSES ONLY AND DOES NOT CONSTITUTE OR FORM PART OF ANY OFFER OR INVITATION TO SELL OR ISSUE, OR ANY SOLICITATION OF ANY OFFER TO PURCHASE OR SUBSCRIBE FOR, ANY NEW ORDINARY SHARES, NOR SHALL IT (OR ANY PART OF IT), OR THE FACT OF ITS DISTRIBUTION, FORM THE BASIS OF, OR BE RELIED ON IN CONNECTION WITH OR ACT AS ANY INDUCEMENT TO ENTER INTO, ANY CONTRACT OR COMMITMENT WHATSOEVER WITH RESPECT TO THE PROPOSEDPLACING. THIS ANNOUNCEMENT IS NOT A CIRCULAR AND INVESTORS SHOULD NOT SUBSCRIBE FOR OR PURCHASE ANY NEW ORDINARY SHARES REFERRED TO IN THIS ANNOUNCEMENT EXCEPT SOLELY ON THE BASIS OF INFORMATION IN THE CIRCULAR EXPECTED TO BE PUBLISHED TODAY. COPIES OF THE CIRCULAR WILL, FOLLOWING PUBLICATION, BE AVAILABLE FROM SILENCE THERAPEUTICS' OFFICES AT22 MELTON STREET, LONDON NW1 2BW.

THE SECURITIES MAY NOT BE OFFERED OR SOLD IN THE UNITED STATES, UNLESS REGISTERED UNDER THE U.S. SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR PURSUANT TO AN EXEMPTION FROM SUCH REGISTRATION. NO PUBLIC OFFERING OF THE SECURITIES DISCUSSED HEREIN IS BEING MADE IN THE UNITED STATES AND THE COMPANY DOES NOT CURRENTLY INTEND TO REGISTER ANY SECURITIES UNDER THE SECURITIES ACT. THE INFORMATION CONTAINED HEREIN DOES NOT CONSTITUTE AN OFFERING OF SECURITIES FOR SALE IN THE UNITED STATES.

SILENCE THERAPEUTICS PLC

("Silence Therapeutics" or the "Company")

Placing of New Ordinary Shares and Share Consolidation

Highlights

·; Gross funds raised £19.025m at 4p per share (pre Share Consolidation price)

·; Net funds raised £18.7m

·; 50 into 1 Share Consolidation

Ali Mortazavi, director of corporate strategy, said: "This capital raise is a significant milestone for Silence Therapeutics and a strong vote of confidence by existing and new institutional shareholders in the Company's technologies."

The Board of Silence Therapeutics is pleased to announce a Placing raising approximately £19 million (before expenses) through the issue of up to 9,512,500 New Ordinary Shares (following the Share Consolidation, described below) by way of a placing to certain investors at the placing price of 200 pence per New Ordinary Share (following the Share Consolidation). The Placing Price represents a discount (on a pre-consolidation basis) of 9.6 per cent. to the closing mid-market price of 4.425 pence on 9 April 2013 (being the last business day prior to this announcement). The Company also announces that it proposes to undertake a Share Consolidation of 1 New Ordinary Share of 5 pence each in nominal value for every 50 Existing Ordinary Shares of 0.1 pence each in nominal value.

The Placing and the Share Consolidation are conditional, inter alia, upon the passing by Shareholders of certain Resolutions at the General Meeting.

The Circular relating to the Placing and Share Consolidation will be posted to Shareholders today. The Circular contains a notice of general meeting to approve, inter alia, the Placing and the Share Consolidation which will be held at the offices of Covington & Burling LLP, 265 Strand, London, WC2R 1BH at 10.00 a.m. on 29 April 2013.

The Circular will soon be available to view on the Company's website (www.silence-therapeutics.com). Copies of the Circular will be also available from the offices of Silence Therapeutics, 22 Melton Street, London NW1 2BW and at the offices of Covington & Burling LLP, 265 Strand, London, WC2R 1BH.

For further information please contact:

Silence Therapeutics plc

Ali Mortazavi, director of corporate strategy T: +44 (0) 333 988 0140

[email protected]

Tim Freeborn, finance director T: +44 (0)333 988 0140

[email protected]

N+1 Singer

Shaun Dobson / Jenny Wyllie T: +44 (0)207 496 3000

[email protected]

[email protected]

Background to and reasons for the Placing

During the last 12 months Silence Therapeutics has made progress in advancing its pipeline and the Company is now focused on creating value by making further advances in all aspects of the business. It is the intention of the Directors that the net proceeds of £18.7 million will be used to support the development of the RNAi platform, to broaden its skills from its pre-clinical research to include clinical and commercial expertise and to fund a Phase Ib/IIa Atu027 programme in pancreatic cancer. These broader skills will be used to add a further indication in Atu027 and to bring drugs targeting non-cancer indications into the clinic. These further trials are likely to use DACC and DBTC in addition to AtuPLEX.

RNAi platform

The Company has an established AtuRNAi patent portfolio, the core technology for developing drugs to silence any human gene. The Directors believe this is one of only two known patented RNAi triggers which have been tested in humans.

Delivery platform

Separately, the Company has developed technologies to deliver the AtuRNAi molecule to target tissues:

·; the AtuPLEX system delivers siRNA to the endothelial cells of the vascular system;

·; the DACC system delivers siRNA efficiently to the vascular endothelium of the lung; and

·; the DBTC system specifically delivers siRNA to hepatocytes and the hepatic vascular system of the liver.

The Company's delivery platforms enable the Company to deliver drugs to a range of target tissues in the body.

Atu027

Atu027, for the treatment of solid tumours, is Silence Therapeutics' most advanced internal drug candidate. Atu027 combines Silence Therapeutics' proprietary drug delivery system AtuPLEX with AtuRNAi, the Company's proprietary RNAi chemistry. Atu027 specifically targets PKN3, a protein, implicated in metastases which is the process responsible for the vast majority of cancer deaths. Atu027 has a novel metastatic effect, preventing the spread of cancer cells into and out of blood vessels. Pre-clinical studies have indicated that Atu027 works by inhibiting blood supply to solid tumours and has a particular profound impact on the prevention and growth of metastases. Combined with other currently marketed anti-cancer drugs, Atu027 has demonstrated additive effects in pre-clinical studies.

Silence Therapeutics is currently conducting a Phase Ib/IIa trial of Atu027 in patients with pancreatic cancer, the first stage of which will run until the second quarter of 2014.

Silence Therapeutics expects to commence a Phase Ib/IIa trial of Atu027 in a second indication in the first quarter of 2014. The Company is also considering a further Phase Ib/IIa trial for a third indication which is expected to commence later in 2014 if, after continually monitoring the results of the first two indications, the Company believes it would justify the capital expenditure. The Company is evaluating a number of options but it is expected that the second indication will be head and neck cancer and the third indication, if it were to proceed, will be breast cancer.

Success in any of these trials will provide a further validation of the AtuPLEX delivery system and could potentially open the way to a large scale maintenance therapy for cancer. The trials have the potential to deliver a value inflexion point for Silence Therapeutics with the next 12-18 months.

DACC

The DACC system delivers siRNA efficiently to the vascular endothelium of the lung. Atu111, which utilises the DACC delivery system, is at the pre-clinical stage of development. The target for this RNAi therapeutic is undisclosed however, pre-clinical models have indicated the ability to inhibit gene expression for up to a month.

In addition to its Atu111 programme, Silence Therapeutics is looking to exploit DACC in other areas of lung disease and is therefore exploring several drug candidates in a variety of lung cancer models.

DBTC

Silence Therapeutics has developed a novel delivery system known as DBTC that enables highly specific delivery of siRNA molecules to cells of the liver including hepatocytes. Silence Therapeutics believes there is a potential role for the DBTC system in delivering RNAi therapies to the liver in the treatment of hypercholestrolaemia. In pre-clinical studies DBTC inhibited gene expression for up to a week.

Advantages of siRNA versus traditional pharma programmes

The Directors believe siRNA has the potential to offer a faster and cheaper way to develop drugs compared to traditional small molecule pharmaceuticals, with the pathway from pre-clinical testing to clinical study of a product expected to cost in the region of €1.9 million and taking between 12 to 22 quarters. With siRNA therapeutics specific genes can be blocked, which should bring a reduced risk of side-effects. Once a gene target is identified, the development timetable is faster than the multiple cycles of optimisation often needed in traditional pre-clinical work. Lastly, the Directors believe the Company's pre-clinical data is a good guide to clinical outcomes due to specificity of the drug whereas long-established industry statistics show a poor correlation between animal studies and clinical outcomes.

Pipeline

As stated above, Silence Therapeutics intends to use the net proceeds of the Placing to carry out further cancer studies using Atu027. Whilst the Company is exploring a number of alternatives, it is expected that these further studies will be in head and neck cancer and breast cancer.

The Company also has two projects, in acute lung injury and hypercholesterolaemia, at pre-clinical stage. Work in six other indications, also targeting the liver and lung, is at proof of concept stage.

In addition to Silence Therapeutics' own programmes, the Company has licensed its RNAi technology to several pharmaceutical companies including Quark and AstraZeneca.

Competitive landscape

Alnylam is one of the only other major recognised companies with the freedom to operate in the siRNA space. Alnylam has a number of RNAi products at various stages of testing including five pre-clinical, two Phase I and two Phase II products. The Directors believe that success for Alnylam in any of these studies would further validate Silence Therapeutics' technology and importantly its strategy.

Use of proceeds

The Company expects to use the net proceeds of the placing of £18.7 million to fund a Phase Ib/IIa programme in Atu027 and to develop its non-cancer projects and broaden its clinical expertise. The Company also expects to use its current cash resources, in addition to the net proceeds, to further develop its non-cancer projects and broaden its clinical expertise.

The net proceeds of the Placing and the Company's existing cash resources are expected to fund a two year spending programme as follows:

Whilst the Group has sufficient cash resources for its near term needs and retains discretion over a substantial part of its development and other expenditure, the Board believes that the Group requires and would benefit from additional finance to enable it to accelerate its product strategy.

If Resolutions 1, 2 and 3 are not passed by Shareholders at the General Meeting, the Placing would be unable to proceed. In this situation the Company would continue to invest its cash resources to complete the Phase Ib/IIa pancreatic trial of Atu027. However the Directors believe that the acceleration of its other drug programmes has the potential to deliver much higher returns for Shareholders.

Information on the Placing

The Company is proposing to raise approximately £19 million by way of a placing of 9,512,500 New Ordinary Shares at a price of 200 pence per New Ordinary Share (following the Share Consolidation). The New Ordinary Shares will represent approximately 20.2 per cent. of the Enlarged Share Capital of the Company. The Placing Price represents a discount of 9.6 per cent. to the Closing Price of 221.25 pence for 50 Existing Ordinary Shares as at 9 April 2013 (being the latest practicable date prior to this announcement).

The New Ordinary Shares will be issued in the form of Consolidated Ordinary Shares following the Share Consolidation and, when issued will be credited as fully paid and will rank in full for all dividends and other distributions declared, made or paid after the admission of the New Ordinary Shares and will otherwise have all the same rights as the Existing Ordinary Shares. As a result of the Share Consolidation, Placees will receive 1 Consolidated Ordinary Share for every 50 New Ordinary Shares offered pursuant to the Placing and will pay 200 pence per Consolidated Ordinary Shares rather than 4 pence per New Ordinary Share.

The New Ordinary Shares are not being made available to the public and are not being offered or sold in any jurisdiction where it would be unlawful to do so.

Application will be made to the London Stock Exchange for the New Ordinary Shares (following the Share Consolidation) to be admitted to trading on AIM. On the assumption that, inter alia, Resolutions 1, 2 and 3 in the Notice of General Meeting are passed, it is expected that admission of the New Ordinary Shares (following the Share Consolidation) will become effective on 30 April 2013.

Immediately following Admission, the Company will have 47,013,554 Consolidated Ordinary Shares in issue. Since the Company currently holds no shares in treasury, the total number of voting rights in the Company immediately following Admission is therefore 47,013,554.

Share Consolidation

The Company intends to consolidate the Existing Ordinary Shares on the basis of 1 Consolidated Ordinary Share for every 50 Existing Ordinary Shares held. The Directors believe that the proposed Share Consolidation is necessary in order to improve the marketability of the shares.

Following the Share Consolidation, and immediately prior to the Placing, the Company will have 37,501,054 Consolidated Ordinary Shares in issue. The Board would like to make it clear that the number of shares held by Shareholders will be reduced by a factor of 50 times compared to that currently held, but that each share will have a higher nominal value. For example if a Shareholder has 100 Existing Ordinary Shares with a nominal value of 0.1 pence each, after the Share Consolidation, the Shareholder will have 2 Consolidated Ordinary Shares with a nominal value of 5 pence each.

The Consolidated Ordinary Shares will have the same rights as the Existing Ordinary Shares including voting, dividend and other rights. Where, as a result of the Share Consolidation, fractional entitlements arise, no fractions of shares will be issued but will be aggregated and sold in the market on behalf of the relevant Shareholder save that, where net proceeds are less than £3.00 per relevant Shareholder (which it is expected will be the case), then the net proceeds of such sale will be retained for the benefit of the Company.

New certificates in respect of the Consolidated Ordinary Shares will be issued following the conclusion of the Placing. After despatch of definitive share certificates, certificates for Existing Ordinary Shares will cease to be valid for any purpose whatsoever.

Shareholders who hold their Existing Ordinary Shares in uncertificated form are expected to have their CREST accounts credited with the Consolidated Ordinary Shares on 30 April 2013. For Shareholders who hold their Existing Ordinary Shares in certificated form share certificates for the Consolidated Ordinary Shares will be despatched by 7 May 2013. Certificates for Existing Ordinary Shares will no longer be valid after 29 April 2013 and should be destroyed upon receipt of certificates in respect of the Consolidated Ordinary Shares. Pending despatch of the definitive certificates in respect of the Consolidated Ordinary Shares, transfers of Consolidated Ordinary Shares held in certificated form will be certified against the register.

Authority for the Share Consolidation will be sought by the proposal of Resolution 1 at the General Meeting.

Irrevocable commitments from certain Directors and major Shareholders

The Directors who in aggregate hold 84,820,000 Existing Ordinary Shares, representing approximately 4.5 per cent. of the existing issued ordinary share capital of the Company, have irrevocably undertaken to vote in favour of the Resolutions at the General Meeting.

Certain major Shareholders, namely Robert Keith, Ora (Guernsey) Limited and Richard Griffiths, who in aggregate hold 997,383,356 Existing Ordinary Shares representing approximately 53.2 per cent. of the existing issued ordinary share capital of the Company, have irrevocably undertaken vote in favour of the Resolutions at the General Meeting.

Current trading and prospects

In April 2013, the Company began dosing patients in its Phase Ib/IIa pancreatic cancer trial. This is a potentially landmark project for Silence Therapeutics. Work continues on assessing a range of microRNA in combination with our delivery platforms. At 31 March, our net cash was over £7 million. This is sufficient to fund the Company until the pancreatic cancer trial produces initial results in mid-2014.

Related party transaction

As part of the Placing, Richard Griffiths and an associated Company, Antisoma plc, are subscribing for 500,000 New Ordinary Shares (following the Share Consolidation) and 2,000,000 New Ordinary Shares (following the Share Consolidation), respectively, at the Placing Price.

Under the AIM Rules, Richard Griffiths, by way of his direct personal holding in shares of the Company and his ownership of a controlling majority of the share capital of ORA (Guernsey) Limited, is deemed to be a related party due to his substantial direct and indirect shareholding in the Company. Antisoma plc, by way of Richard Griffith's ownership of a controlling majority of the share capital of ORA (Guernsey) Limited, is an associate of Richard Griffiths. As such, the participation of Richard Griffiths and his associate Antisoma plc in the Placing is deemed to be a related party transaction.

The Directors consider, having consulted with N+1 Singer, that the terms of the Placing are fair and reasonable insofar as Shareholders are concerned. In providing advice to the Directors, N+1 Singer has taken into account the commercial assessments of the Directors.

Recommendation

The Directors believe that the Placing and the Share Consolidation and therefore the Resolutions are in the best interests of the Company and Shareholders taken as a whole. The Directors therefore unanimously recommend that you vote in favour of the Resolutions to be proposed at the General Meeting, as they intend to do in respect of their own shareholdings.

General Meeting

A notice convening a General Meeting of the Company to be held at 10 a.m. on 29 April 2013 at the offices of Covington & Burling LLP at 265 Strand, London, WC2R 1BH, is being sent to Shareholders shortly, at which the Resolutions (summarised below) will be proposed:

Resolution 1

An ordinary resolution to undertake the Share Consolidation.

Resolution 2

An ordinary resolution to authorise the Directors to allot New Ordinary Shares at 200 pence per share up to a maximum nominal amount of £475,625.00 pursuant to the Placing. This Resolution is conditional upon Resolution 1 becoming unconditional.

Resolution 3

A special resolution, pursuant to section 571 of the Companies Act, to disapply the statutory pre-emption rights on the allotment of equity securities, pursuant to the authority contained in Resolution 2. This Resolution is conditional upon Resolutions 1 and 2 becoming unconditional.

Resolution 4

An ordinary resolution to authorise the Directors to allot relevant securities for the purposes of section 551 of the Companies Act provided that such power be limited to the allotment of new Consolidated Ordinary Shares up to an aggregate nominal amount of £352,601.66 (representing 15 per cent. of the Enlarged Share Capital at Admission). This Resolution is conditional upon the passing of Resolution 1 and upon such Resolution becoming unconditional.

Resolution 5

A special resolution to grant the Directors authority to allot equity securities for cash as if section 561 of the Companies Act did not apply to such allotment provided that such power shall be limited to the allotment of new Consolidated Ordinary Shares up to an aggregate nominal amount of £352,601.66 (representing 15 per cent. of the Enlarged Share Capital at Admission). This Resolution is conditional upon the passing of Resolutions 1 and 4 and upon such Resolutions becoming unconditional.

The authorities in Resolutions 2, 3, 4 and 5 will expire (unless previously revoked or varied by the Company in a general meeting) on the date 15 months from the passing of such Resolutions or at the conclusion of the next annual general meeting, whichever occurs first. The authority and power in Resolutions 2 and 3 are in addition to the authority and power to be conferred upon the Directors pursuant to Resolutions 4 and 5. The authority and power in Resolutions 4 and 5 will replace all other existing authorities and powers previously conferred on the Directors (with the exception of Resolution 2 and 3 above) including the authorities and powers granted at the General Meeting of the Company held on 31 July 2012.

Expected timetable of principal events

Notes:

(1) References to times in this Announcement are to London time (unless otherwise stated).

(2) If any of the above times or dates should change, the revised times and/or dates will be notified by an announcement to an RIS.

(3) The dates and timing of the events in the above timetable and in the rest of this Announcement is indicative only and may be subject to change.

Defined terms in this announcement take the same meaning as set out in the Circular.