Lord Ashcroft, the controversial Tory tycoon who ploughed millions into the drive to win dozens of marginal seats, has written a hard-hitting verdict of the "tactical errors" that denied David Cameron outright victory at the general election in May.
The billionaire donor has told the Prime Minister he will resign as deputy chairman of the Conservative Party at its board meeting in eight days' time.
In a punishing parting shot, he will tomorrow publish a frank critique of an election campaign that missed an "open goal" and failed to convert double-digit poll leads into an overall parliamentary majority.
Lord Ashcroft's 133-page book, Minority Verdict: The Conservative Party, the Voters and the 2010 Election will highlight a string of mistakes, including: the failure to get the Tory "message" and "brand" across to the voters; relentless "counterproductive" attacks on the Labour Party and its leader, Gordon Brown; agreeing to a televised debate of political leaders, which enabled the Liberal Democrats – and particularly their leader, Nick Clegg – to seize the initiative.
Lord Ashcroft, 64, who has put at least £10m into Tory coffers in recent years, has masterminded a long-term strategy to target marginal seats held by other parties.
Although the peer praises Mr Cameron's contribution to the election campaign and says the party should feel "proud" of the result, he complains that the poll leads of the previous two years should have produced a "thumping majority".
He writes: "The Conservative Party faced a shambolic government, an unpopular prime minister, a recession, a huge budget deficit and an overwhelming national desire for change.
"A year before the election the Conservatives were 20 points ahead in the polls, yet they failed to win an overall majority. Surely this had been an open goal. How could they come so close to missing?"
Lord Ashcroft raises doubts over central elements of the Tory operation. The campaign to force Mr Brown into agreeing to a televised leaders' debate was seen as a masterstroke at the time, as it was assumed that the quick-witted Mr Cameron would leave the Labour leader standing. But the strategy did not reckon with the benefit the debates would offer to Mr Clegg, who used the exposure to elevate his public persona massively during the early days of the campaign.
Similarly, the brutal focus on Mr Brown's failings had been regarded as a simple way of convincing voters that Mr Cameron offered a fresher, younger alternative.
But, in his "first and only contribution" to the debate on the subject, Lord Ashcroft concludes: "At a national level, too much of our message was focused on unnecessary and counterproductive attacks on Gordon Brown and Labour, which meant that voters were not clear about our own plans.
"We did not make as much progress as we should have done in transforming the party's brand, and in reassuring former Labour voters that we had changed and were on their side.
Lord Ashcroft has also made clear his frustration that he did not receive greater support from the party leadership when he was forced to admit in March that he had "non-dom" status and had not been paying income tax on his worldwide earnings.
"They could have mounted a more spirited defence of the situation," he told The Sunday Telegraph. "It did prove to me that the Labour attack team was much more effective than the Conservative defence team."Reuse content