Chancellor George Osborne has told the Conservative Party that ditching its support for equal marriage could cause a catastrophic defeat at the 2015 general election.

Writing in The Times on Tuesday, the chancellor drew parallels between the position of the Tories and the Republican Party in the United States.

Mr Osborne said the Republicans had lost “swathes of voters” last week because of their opposition to equal marriage and abortion rights for women.

Invoking the rhetoric of Margaret Thatcher’s 1979 election manifesto, Mr Osborne urged his party to get in step with people and “how they want to live their lives”.

The chancellor said: “It is astonishing that Mr Romney won the election among men by a clear-cut margin of 7%; but it was Mr Obama’s 11% lead among women that won it for the president, even though many of those that voted Democrat thought Mr Romney would manage the economy better.

“President Obama’s high-profile endorsement of equal marriage for gay couples also enthused younger voters.

“But polls found that a majority of all Americans supported him on the issue and voted for it in all four states that held ballots”.

The chancellor, who came out in support of equal marriage on the eve of October’s Conservative Party Conference, added:

“I strongly support gay marriage on principle. Of course in Britain these issues are ones of individual conscience and free votes, but I am proud to be part of a government that will introduce a bill to allow gay marriage.

“It is worth reflecting that in Britain, as in America, a clear majority of the public support gay marriage, and an even bigger majority of women support it. That majority support is just as high in the north as it is the south, and it is equally high among all socio-economic groups”.

Last month, in a letter to the former Welsh Secretary Cheryl Gillan, Prime Minister David Cameron talked of same-sex marriage being “popular” with the electorate and made a similar argument over polling data.

The PM said: “I firmly believe that the government’s proposals are entirely consistent with Conservative values, and that is why I will be supporting them.”