TR-1: Notification of Major Interest in Shares

3rd Aug 2012 17:35

For filings with the FSA include the annex For filings with issuer exclude the annex

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARESi

1. Identity of the issuer or the underlying issuer SILENCE THERAPEUTICSof existing shares to which voting rights are

PLCattached:ii

2 Reason for the notification (please tick the appropriate box or boxes): An acquisition or disposal of voting rights

An acquisition or disposal of qualifying financial instruments which may result

in the acquisition of shares already issued to which voting rights are attached

An acquisition or disposal of instruments with similar economic effect to Xqualifying financial instruments An event changing the breakdown of voting rights

Other (please specify):

3. Full name of person(s) subject to the

ROBERT KEITHnotification obligation:iii 4. Full name of shareholder(s) Rock ( Nominees) Limited (if different from 3.):iv

5. Date of the transaction and date on which the threshold is crossed or

02.08.12reached: v

6. Date on which issuer notified:

03.08.12

7. Threshold(s) that is/are crossed or

18%reached: vi, vii 8. Notified details:

A: Voting rights attached to shares viii, ix Class/type Situation previous Resulting situation after the triggering transaction of to the triggering shares transaction Number Number Number Number of voting % of voting rights x if possible of of of shares rights using Shares Voting the ISIN Rights Direct Direct xi Indirect Direct Indirect CODE xii GB0008433350 54,089,628 3.68% 254,089,628 254,089,628 17.33%

B: Qualifying Financial Instruments Resulting situation after the triggering transaction

Type of Expiration Exercise/ Number of voting % of voting financial date xiii Conversion Period xiv rights that may be rights instrument acquired if the instrument is exercised/ converted. C: Financial Instruments with similar economic effect to Qualifying Financial Instruments xv, xvi

Resulting situation after the triggering transaction Type of Exercise price Expiration Exercise/ Number of voting rights % of voting rights financial date xvii Conversion instrument refers to xix, xx instrument period xviii Nominal Delta Spreadbet n/a n/a n/a 14,236,216 0.97% 0.97% Total (A+B+C) Number of voting rights Percentage of voting rights 268,325,844 18.30%

9. Chain of controlled undertakings through which the voting rights and/or the financial instruments are effectively held, if applicable: xxi

Proxy Voting: 10. Name of the proxy holder:

11. Number of voting rights proxy holder will cease

to hold:

12. Date on which proxy holder will cease to hold

voting rights: 13. Additional information: 14. Contact name: ROBERT KEITH

15. Contact telephone number:

0207 491 0581

Note: Annex should only be submitted to the FSA not the issuer Annex: Notification of major interests in sharesxxii

A: Identity of the persons or legal entity subject to the notification

obligation Full name

(including legal form of legal entities)

Contact address

(registered office for legal entities)

Phone number & email Other useful information

(at least legal representative for legal persons)

B: Identity of the notifier, if applicable

Full name Contact address Phone number & email Other useful information (e.g. functional relationship with the person or legal entity subject to the notification obligation) C: Additional information

For notes on how to complete form TR-1 please see the FSA website.

XLON

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Related Shares:

SLN.L