Lord Ashcroft to quit as Conservative deputy chairman
Conservative Party deputy chairman Lord Ashcroft is to quit the role he has held since 2005.
He is expected to stand down at the next meeting of the party board on 27 September - less than a week before the party conference.
The businessman and politician is the party's biggest single donor, and reportedly has a fortune of £1.1bn.
A Conservative Party spokesman said it was "extremely grateful for his tireless work".
"He has made a very significant contribution to the success of the Conservative Party and we thank him for his work and dedication," a spokesman said.
Lord Ashcroft, 64, has been Tory deputy chairman since 2005, having previously been party treasurer from 1998 to 2001.
As treasurer, responsible for fund-raising, Mr Ashcroft was said to have widened the party's pool of donors and allowed it to recruit more staff.
The powerful party figure was credited with devising its marginal seat strategy, pouring resources into constituencies where Labour MPs defended small majorities.
He has published several books including, in 2005, Smell the Coffee: A wake-up call for the Conservative Party.
In his latest - Minority Verdict: The Conservative Party, the voters and the 2010 election - he criticises the party's election campaign, particularly the participation in televised leaders' debates, and "counterproductive attacks" on the Labour Party and Gordon Brown, the Sunday Telegraph reported.
He also said the party failed to get its "message" and "brand" across to voters.
"The debates were arguably a tactical error which exposed a strategic problem: three weeks before the election the market was still wide open for a party of change.
"[Liberal Democrat leader] Nick Clegg was only able to appropriate the territory of 'real change' because we did not dominate it ourselves," Lord Ashcroft was quoted as saying in the Sunday Telegraph.
A party spokesman said: "This book is part of the 'lessons learnt' exercise and we should welcome it."
Lord Ashcroft praised Mr Cameron's personal contribution to the election campaign and said the party should feel "proud" of the result, the Sunday Telegraph reported.