Cameron will not offer marriage tax breaks to placate anti-gay marriage Tories, says Government source

Pledge was made in Tory manifesto and coalition agreement

So far 233 MPs have come out in favour of gay marriage (Getty Images)

David Cameron may have more trouble with backbenchers after the revelation that tax breaks for married couples will not be included in next month's Budget.

The Conservatives' 2010 manifesto pledged to introduce the tax break, which also made it into the coalition agreement.

It would involve allowing one member of a married couple or civil partnership to transfer £750 of their tax-free personal allowance to their partner, would be worth around £150 a year to basic-rate taxpayers.

The government's failure to bring in the tax breaks so far has angered many in the party, and a number of backbenchers have suggested the change should be included in George Osborne's Budget next month in return for their supporting controversial plans to introduce gay marriage.

But a senior Government source told the Press Association that there was no such deal, and ruled out a marriage tax break featuring in this budget.

"It won't be in the Budget but it will be in this Parliament," the source said. "This Budget obviously, with all that has happened in recent weeks and months, will be very much focused on growth in the economy".

Mr Cameron views the introduction of same-sex marriage - which is expected to split his MPs when it is put to a Commons vote next week - as the "Conservative Party delivering the promise it made".

"This is a difficult issue for some in the Conservative Party and he understands the strong feelings that people have, and of course it's a free vote," the source said.

"He is proud of the fact that it's a coalition government with strong Conservative participation that is bringing forward a modern and progressive change."

Backbenchers are also said to be questioning Osborne's position, as the economy remains stagnant.

But the same senior source insisted that Mr Osborne had the "full confidence" of the Prime Minister.

"He is an extremely successful Chancellor. He is battling very difficult economic circumstances," the source said. "George Osborne will be Chancellor at the next general election."

The developments came amid fevered speculation over plots against the Prime Minister, with suggestions rebels have set a deadline of summer 2014 for the party's electoral fortunes to turn around.

Tory MP David Burrowes told The Times: "There's serious unrest in the grassroots. You cannot avoid the fact that the troops are unhappy. People are drifting away."

Backbenchers insist the issue has sparked "serious unrest" among the party's rank and file and are claiming some constituencies have lost as many as 100 members each. Conservative headquarters, however, does not hold up-to-date membership records, the newspaper said.