Prime minister David Cameron and Chancellor George Osborne are reportedly under mounting pressure to give married couples a tax break in order to secure support for their same-sex marriage bill.

The Conservative Party promised a tax break on married and civil partnered couples at the last election but coalition partners the Liberal Democrats oppose the move.

Now, Mr Cameron and Mr Osborne, joint supporters of the Marriage (Same-sex couples) Bill to be voted on next week are being called upon to grant a tax break in order to secure backbench votes.

Former minister Sir Gerald Howarth told The Times: “What quid pro quo is there for us? Implementing a manifesto commitment should come before implementing something for which there’s no mandate, let alone public consent, and which has the added disadvantage of being deeply resented by longstanding, hard-working Conservative members who feel they are being trampled on.”

The Chancellor will be announcing the Budget in March and MPs are hoping that he will reward married couples. A cabinet source told the Times that Mr Osborne should act ““sooner rather than later” and that the Budget would be “a good time to placate an awful lot of people”.

Although the Conservative party are preparing for as many as 150 of the 303 Tory MPs to vote against same-sex marriage, some predict that that the level of the opposition will be lower than expected.

Owen Paterson, the Environment Secretary, Philip Hammond, the Defence Secretary, and Chris Grayling, the Justice Secretary are all expected to vote against the bill. It has been proposed by Conservatives Maria Miller, the Culture Secretary, Mr Cameron, Mr Osborne, Eric Pickles, Theresa May and Michael Gove.