Liberal Democrat leader and Deputy Prime Minister Nick Clegg says he will not allow Tory opponents to succeed in wrecking the Marriage (Same Sex Couples) Bill.

Three Tory MPs who are against marriage rights for gay couples – Tim Loughton, Charlotte Leslie and Rob Wilson – are pushing for civil partnerships to be an option for heterosexual couples in an amendment which has widespread support from both supporters and detractors of equality.

However, some in Westminster fear the amendment is an attempt to “wreck the bill” because it could delay its passage beyond the 2015 general election.

Earlier, Culture Secretary and Minister for Equalities, Maria Miller, warned that the amendment was a “complicated distraction”.

Mr Clegg said it was Lib Dem policy that civil partnerships should be available to heterosexual couples but said he would not back amendments that would derail the bill.

Speaking at a Nacro event in London, he said: “The bottom line is I will do whatever I judge is best to safeguard the bill and to make sure it doesn’t become hijacked by those whose ulterior motive is actually to discredit or to derail the legislation.”

He added: “In principle this is something we have long supported but I don’t want to lose the wood for the trees. I want this bill to be passed and for the bill to do what it says on the tin which is to provide equal rights to marriage for same sex couples and that will be my overriding objective.”

The bill will be debated from Monday, with its third reading on Tuesday. If approved, it will go to the House of Lords on Wednesday.

Liberal Democrat leader and Deputy Prime Minister Nick Clegg told PinkNews last December that he was hopeful the first same-sex marriages would be able to take place by the summer of 2013.

But on Monday, Maria Miller stated that the eventual date for this would be “next summer”.