The move marks a swift return for Baverstock to party politics. He was director of strategic communications at Conservative Central Office under doomed former leader Iain Duncan Smith, but was ousted when Michael Howard replaced IDS.
Baverstock, who once stood as a Labour councillor before becoming "disillusioned" with New Labour, told PRWeek: "I am handling strategy, polling and messaging for the Clarke campaign." His former deputy at Central Office, Richard Chalk, is overseeing press relations for the Clarke campaign, while MP Andrew Tyrie is acting as campaign manager.
Ketchum London CEO David Gallagher said it would not replace Baverstock, who is officially on gardening leave.
A BBC poll this week showed Clarke as runaway favourite among the public.
It emerged this week the contest could yet depend on securing the support of constituency party chairmen as well as Tory MPs.
Frontrunner David Davis is being advised by long-time associate Fleishman-Hillard UK chief Kevin Bell, F-H senior consultant Gavin Megaw and ex-Central Office staffer David Hart.
David Cameron is aided by George Eustace and backed by former Consolidated Communications director Ed Vaizey, now an MP.
Baverstock joined Ketchum in February 2004.
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