Lord Ashcroft, the former deputy chairman of the Conservative Party who has refashioned himself as a influential impartial pollster, told a meeting in Westminster earlier this month that the "abuse" hurled at Ukip supporters by the Tories had backfired.
The peer's detailed surveys of marginal constituencies have become a must-read for MPs in the run-up to the general election.
"So now we have a great idea that we should now say a vote for Ukip is a vote for Miliband, of course they'll understand that. The problem is what politicians often say and what the voters hear are very different. We hold focus groups on this," he said.
"What do they really hear? They hear two fingers pointed at them, saying: 'oi sunshine, when you wake up and realise how dumb, dumb, dumb you are, do you know what you are going to do, you are going to be back voting for me'."
The comments are also reported in The Independent today. The Huffington Post has obtained audio recording of the event hosted by the 'Conservative Voice' group in parliament on 5 November. Several Tory MPs were present to listen to the attack on their party's strategy, including eurosceptics Peter Bone and David Nuttall.
Ashcroft warned the MPs that the decision of the Tory leadership and campaign machine to attack Ukip supporters had failed. "They went through abuse from the Conservatives. The strategy was to call them fruitcakes, nutters, closet racists, you name it."
"So now you've got this group of Ukip voters, 95% of whom are decent people, you abuse them you thrash them and then you tell them they are coming home to daddy?"
A Ukip spokesperson said: "Astonishingly there seems to a be a Conservative who actually gets it. Fortunately there seems to be precious little chance of him being listened to be anyone in any position of responsibility in the Conservative party."
Ashcroft has donated millions to the Conservatives in his time, was reported to have stopped giving money in 2011 in frustration at the direction Cameron was taking the party. However the peer is said to have recently resumed funding the Tories.
He also warned that most voters do not believe Cameron will keep his promise to hold a in/out referendum on the EU. "There isn't that degree of trust because he keeps shifting, he will not say where my 'red lines' are," he said.
"Conservatives have no definitive position on it other than we will do something vague and when we have done something vague we will think about what that means and then we will put it to the electorate sometimes in the future but before man gets to the moon again."
Nuttall told HuffPost: "If people want to have their say on our membership of the EU the only realistic way that is going to be achieved is by having a majority Conservative Government elected next May.
"My message to anyone who is concerned about immigration or the fact that too many powers have been passed to Brussels the answer is to vote Conservative. Once faced with a choice between a Labour Government which will not give them a vote on the EU and a Conservative one that will I have every confidence the British people will choose to elect a Conservative Government."
Mark Reckless, the former Tory MP who defected to Ukip, is expected to easily win the by-election in his Rochester constituency today. He will become Nigel Farage's party's second ever elected MP. Defeat for the Conservatives will be a damaging blow for the prime minister.