LONDON (Reuters) - Ford Motor Company F.N said on Saturday it will take bids on some of its advertising managed by WPP WPP.L, adding to uncertainty around the British ad giant after last week's exit of founder Martin Sorrell.

The Ford logo is seen at the New York Auto Show in the Manhattan borough of New York City, New York, U.S., March 29, 2018. REUTERS/Shannon Stapleton/File Photo

While Ford’s decision does not affect all of its accounts with WPP - and the agency will be able to bid for the rest of the business along with everyone else - it comes at a difficult juncture for the world’s biggest advertising firm.

Sorrell, who over 33 years built the firm into one of Britain’s biggest companies, quit last week as chief executive officer after an allegation of personal misconduct that he denies.

Saturday’s announcement is part of a review of Ford’s strategy that has lasted since November, when it told long-time partner WPP that it was considering its future ad model.

“We are going to place some portions of our advertising business up for bid with other agencies, including WPP, beginning in the coming weeks. No decisions have been made,” Ford Britain said in a statement.

It added that WPP is a trusted partner of Ford and that it had offered the agency more detail about its marketing aspirations.

WPP, which counts Ford as a major client, declined to comment.

WPP staff were sent a memo on Friday outlining Ford’s decision.

“WPP will have an opportunity to compete with other firms to retain these portions of the business, and will remain Ford’s agency of record in some other key areas,” a copy of the memo seen by Reuters said.

Ford’s review of its ad operations does not include accounts with WPP in China, public affairs, U.S. dealerships or WPP’s Hudson Rouge agency that handles Ford’s luxury Lincoln brand, the memo said.

WPP and its major rivals Omnicom OMC.N, Publicis PUBP.PA and IPG IPG.N face challenges on every front, from the might of Google and Facebook - whom Sorrell famously dubbed "frenemies" - to the rapidly encroaching consultants Accenture and Deloitte.

With clients demanding ever-lower fees, big advertising groups are grappling to become more nimble and efficient to protect their revenues and avoid pressure on them to break up.