The Conservative Party will become unelectable if it fails to unite behind plans to introduce gay marriage, a cabinet minister is expected to warn.
Cabinet Office minister Francis Maude will warn MPs in his party that if they fail to support coalition plans to legislate for same sex marriage the public will view them
"The Conservative Party will always suffer if it is seen as if it is trying to turn the clock back to an imagined golden era. You can’t drive policy looking through a rose-tinted rear-view mirror," he will say in a speech on Wednesday.
"If we are seen as being defined by backward-looking social attitudes we will be seen as unacceptable and unelectable."
He will add: "We shouldn’t arrogantly assume we always know best and that society should conform to our expectations rather than us adapting to evolving social norms."
Maude's intervention comes after a blistering attack on gay marriage by the leader of the Catholic Church in Scotland, Cardinal Keith O'Brien, who said it would lead to the immoral degeneration of society.
According to the Daily Mail, Maude will say that the death of his brother from Aids in the 1990s convinced him that the Conservative Party's opposition to gay rights was wrong and was an unacceptable "attitude of intolerance".
The government is on a collision course with many of its own MPs over the issue, with some Tory backbenchers voicing vocal opposition to the plans.
Peter Bone has described gay marriage as "nuts" while Fiona Bruce said she opposed it "as a mother".
And the paper reports that the Horsham MP will point out that the party should embrace change just as it had by being the first British party to elect a female prime minister.
The Daily Telegraph reports that Maude will say the party should be a "phoenix not a dodo" and has to modernise to survive.
"When we have failed to do so - when we failed to understand and influence the spirit of the age - the electorate rightly punished us," he will say.
Maude has long been seen as a moderniser having once been a right-wing Thatcherite. He angered many of its more traditional members in 2005, when party chairman, he said voters saw the Conservatives as "out of touch".
In 2002 he defied a three-line whip imposed by the then leader Iain Duncan Smith and voted in favour same-sex couples to adopt children.
David Cameron backed plans to introduce gay marriage in his party conference speech last year. He told his party that they should support the move as it encouraged stability and commitment between couples.