Conservative Treasury Minister David Gauke says the government is “firmly committed” to recognising marriage in the tax system – a move which would benefit those in civil partnerships, heterosexual and same-sex marriages – once the Marriage (Same Sex Couples) Bill becomes law.

In their 2010 general election manifesto, the Conservatives said recognising marriage and civil partnerships in the tax system would “send an important signal that we value couples and the commitment that people make when they get married”.

But so far the policy has not been introduced.

Under plans being considered, married couples where one partner does not work could get a tax break of £150 a year.

In a letter to Conservative MPs Treasury Minister David Gauke did not spell out what the proposal would be, but sets out the 2010 manifesto commitment that a non-working member of a married couple or civil partnership would be able to move £750 of their tax-free allowance to their working partner, worth about £150 a year to basic-rate taxpayers.

“The prime minister has always been clear that it is important to recognise marriage in the tax system, and this firm commitment remains,” Mr Gauke said in his letter – published by The Spectator.

He added: “An announcement on details of how we will legislate for this in this Parliament will be made by the chancellor in due course.”

Conservative MPs are calling on ministers to signal a firm date when the measure – which is opposed by their Lib Dem coalition partners – will be brought forward.

A backbench amendment has been tabled to the Finance Bill by the same-sex marriage opponent and former children’s minister Tim Loughton “to restore a transferable married couple’s tax allowance and send out a clear message that we value marriage and family socially and financially.”

Bournemouth West MP Conor Burns, a strong supporter of equal marriage, believes honouring the commitment could help heal division in the Conservative Party following its split on equal marriage.

“One point of sympathy that I have with people who write to me about the [same-sex marriage] bill is that we’re introducing something which was not a manifesto commitment,” he said to PinkNews.co.uk.

“Something that was a manifesto commitment was to introduce recognition of marriage in the tax system. I think it would have been a lot easier to defend the bill if simultaneously we had brought in recognition of marriage in the tax system – and that recognition of marriage in the tax system would have honoured a manifesto commitment and recognised all marriages: gay or straight.

“I think it would have made it a lot easier for the prime minister to say ‘I am supporting marriage’ and as he said very powerfully at conference a few years ago a commitment is a commitment whether it’s between ‘a man and a woman, a women and a women, or a man and a man’.”