Holding(s) in Company

NOTIFICATION OF MAJOR HOLDINGS (to be sent to the relevant issuer and to the FCA in Microsoft Word format if possible)i

1a. Identity of the issuer or the underlying issuer of existing shares to which voting rights are attachedii:

Mereo BioPharma Group plc

1b. Please indicate if the issuer is a non-UK issuer (please mark with an "X" if appropriate)

Non-UK issuer

2. Reason for the notification (please mark the appropriate box or boxes with an "X")

An acquisition or disposal of voting rights

X

An acquisition or disposal of financial instruments

X

An event changing the breakdown of voting rights

N/A

Other (please specify)iii:

N/A

3. Details of person subject to the notification obligationiv

Name

Baker Bros. Advisors LP

City and country of registered office (if applicable)

New York, New York USA

4. Full name of shareholder(s) (if different from 3.)v

Name

Baker Brothers Life Sciences, L.P. and 667, L.P.

City and country of registered office (if applicable)

Delaware USA

5. Date on which the threshold was crossed or reachedvi:

03/06/2020

6. Date on which issuer notified (DD/MM/YYYY):

05/06/2020

7. Total positions of person(s) subject to the notification obligation

% of voting rights attached to shares (total of 8. A)

% of voting rights through financial instruments(total of 8.B 1 + 8.B 2)

Total of both in % (8.A + 8.B)

Total number of voting rights of issuervii

Resulting situation on the date on which threshold was crossed or reached

9.39%

0%

9.39%

213,652,487

Position of previous notification (if

applicable)

N/A

N/A

N/A

8. Notified details of the resulting situation on the date on which the threshold was crossed or reachedviii

A: Voting rights attached to shares

Class/type ofshares

ISIN code (if possible)

Number of voting rightsix

% of voting rights

Direct

(Art 9 of Directive 2004/109/EC) (DTR5.1)

Indirect

(Art 10 of Directive 2004/109/EC) (DTR5.2.1)

Direct

(Art 9 of Directive 2004/109/EC) (DTR5.1)

Indirect

(Art 10 of Directive 2004/109/EC) (DTR5.2.1)

GB00BZ4G2K23

20,061,437

9.39%

SUBTOTAL 8. A

20,061,437

9.39%

B 1: Financial Instruments according to Art. 13(1)(a) of Directive 2004/109/EC (DTR5.3.1.1 (a))

Type of financial instrument

Expirationdatex

Exercise/Conversion Periodxi

Number of voting rights that may be acquired if the instrument is

exercised/converted.

% of voting rights

CONVERTIBLE NOTE 10% 6/2023

6/2023

Not convertible until the underlying shares are authorized by a shareholder vote

0

0%

Warrants @ GBP 0.348 Expiring 8/8/2025

8/8/2025

Not exercisable until the underlying shares are authorized by a shareholder vote

0

0%

SUBTOTAL 8. B 1

0

0%

B 2: Financial Instruments with similar economic effect according to Art. 13(1)(b) of Directive 2004/109/EC (DTR5.3.1.1 (b))

Type of financial instrument

Expirationdatex

Exercise/Conversion Period xi

Physical or cash

settlementxii

Number of voting rights

% of voting rights

SUBTOTAL 8.B.2

N/A

N/A

9. Information in relation to the person subject to the notification obligation (please mark the

applicable box with an "X")

Person subject to the notification obligation is not controlled by any natural person or legal entity and does not control any other undertaking(s) holding directly or indirectly an interest in the (underlying) issuerxiii

Full chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held starting with the ultimate controlling natural person or legal entityxiv (please add additional rows as necessary)

X

Namexv

% of voting rights if it equals or is higher than the notifiable threshold

% of voting rights through financial instruments if it equals or is higher than the notifiable threshold

Total of both if it equals or is higher than the notifiable threshold

Baker Bros. Advisors (GP) LLC

9.39%

0.0%

9.39%

Baker Bros. Advisors LP

9.39%

0.0%

9.39%

Baker Brothers Life Sciences, L.P.

8.71%

0.0%

8.71%

10. In case of proxy voting, please identify:

Name of the proxy holder

N/A

The number and % of voting rights held

The date until which the voting rights will be held

11. Additional informationxvi

Baker Bros. Advisors LP (the "Adviser") is the investment adviser of Baker Brothers Life Sciences, L.P., and 667, L.P. (collectively, the "Funds") and, pursuant to management agreements between the Adviser, the Funds and the respective general partners of the Funds, has complete and unlimited discretion and authority with respect to the Funds' investments and voting power over investments.

Place of completion

New York, New York USA

Date of completion

June 5, 2020