The Conservative leader said the campaign marked the "end of New Labour".

And he vowed that he would not betray the trust of the thousands of voters who turned out to vote Conservative for the first time.

He said that he would now work to put together a "broad coalition" to oust the Labour Government and secure a return to power for the Tories at the next general election.

"Just like in the local elections, just like in the London mayoralty election, thousands of people came to vote for the Conservative Party for the first time and my message to those people is 'We will not let you down'," he told reporters as he left his west London home en route for Crewe.

"I want to go on building this broad coalition for change so we can bring our country better government," he said.

Mr Cameron said Labour had paid the price for running a "backward-looking and divisive" campaign, which focused heavily on Mr Timpson's background, attacking him as a "toff".

"It was in many ways the end of New Labour. I think it was a great mistake," he said.

Labour deputy leader Harriet Harman said people had used the vote to register their concerns about the economy, amid rising food and fuel prices.

"I think that is the message to us very loud and clear," she told Sky News. "Our response will be to listen to people's concerns, to recognise that people are worried about their prospects for the future and to act on their concerns to re-double our efforts."