UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of August 2015.

Commission File Number: 001-35265

CSR plc

(Translation of registrant’s name into English)

Churchill House

Cambridge Business Park

Cowley Road

Cambridge CB4 0WZ

United Kingdom

Tel: +44 (0) 1223 692000

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F x Form 40-F ¨

Indicate by checkmark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(l): ¨

Indicate by checkmark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ¨

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes ¨ No x

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): Not Applicable

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION IN ANY JURISDICTION WHERE TO DO SO WOULD CONSTITUTE A VIOLATION OF THE RELEVANT LAWS OF SUCH JURISDICTION

7 August 2015

CSR plc (“CSR”)

Disclosure of Issued Shares Pursuant to Rule 2.10

In accordance with Rule 2.10 of the City Code on Takeovers and Mergers (the “Code”), CSR confirms that, as at the date of this announcement, it has in issue 166,957,177 ordinary shares (excluding the shares held in treasury) of 0.1 pence admitted to trading on the main market of the London Stock Exchange under the International Securities Identification Number (“ISIN”) GB0034147388.

CSR has an American Depositary Receipts (“ADR”) programme for which JPMorgan Chase acts as Depositary. 1 ADR represents 4 ordinary shares of CSR. The ADRs trade on the NASDAQ Global Select Market of NASDAQ Stock Market LLC. The trading symbol for these securities is CSRE and the ISIN is US12640Y2054.

Enquiries:

CSR: Will Gardiner, Chief Financial Officer +44 (0) 1223 692 000

FTI Consulting: Charlie Palmer +44 (0) 20 3727 1000

CSR plc

(Registrant)

Date: August 7, 2015

/s/ Brett Gladden

Brett Gladden

Company Secretary

CSR PLC 6-K