Holding(s) in Company

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARES

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

Spirent Communications plc

2 Reason for the notification (please tick the appropriate box or boxes):

An acquisition or disposal of voting rights

X

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 qualifying financial instruments

X

An event changing the breakdown of voting rights

X

Other (please specify):

3. Full name of person(s) subject to the notification obligation: iii

BlackRock, Inc.

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

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

20th May 2010

6. Date on which issuer notified:

24th May 2010

7. Threshold(s) that is/are crossed or reached: vi, vii

Holding has gone above 17%

8. Notified details:

A: Voting rights attached to shares viii, ix

Class/type of shares

if possible using the ISIN CODE

Situation previous to the triggering transaction

Resulting situation after the triggering transaction

Number of Shares

Number of Voting Rights

Number of shares

Number of voting rights

% of voting rights x

Direct

Direct xi

Indirect xii

Direct

Indirect

GB0004726096

78,962,774

78,962,774*

N/A

N/A

78,519,727

N/A

11.62%

* Situation previous disclosure is based upon share capital of 678,831,250 while the resulting situation disclosure is based upon share capital of 675,855,578

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financial instrument

Expiration date xiii

Exercise/ Conversion Period xiv

Number of voting rights that may be acquired if the instrument is exercised/ converted.

% of voting rights

C: Financial Instruments with similar economic effect to Qualifying Financial Instruments xv, xvi

Resulting situation after the triggering transaction

Type of financial instrument

Exercise price

Expiration date xvii

Exercise/ Conversion period xviii

Number of voting rights instrument refers to

% of voting rights xix, xx

CFD

N/A

N/A

N/A

36,853,797

Nominal

Delta

5.45%

5.45%

Total (A+B+C)

Number of voting rights

Percentage of voting rights

115,373,524

17.07%

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

BlackRock Investment Management (UK) Limited - 115,373,524 (17.07%)

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:

BlackRock Threshold Reporting Team

14. Contact name:

Stuart Watchorn

15. Contact telephone number:

020 7743 5741; [email protected]

C: Additional information

Contact at Issuer: Michelle Balch, Assistant Company Secretary, Spirent Communications plc

Telephone: 01293 767676