Labour has launched a bid to protect the Marriage (Same Sex Couples) Bill, amid fears that a “wrecking amendment” extending civil partnerships to heterosexual couples could stall the legislation.

The party has put forward its own Manuscript Amendment, which aims to start an immediate consultation on civil partnerships for straight couples, it can only be considered if Culture Secretary and Minister for Equalities, Maria Miller’s amendment for a future review on civil partnerships is approved.

Labour MP Chris Bryant told PinkNews.co.uk: “We don’t want to do anything to put the bill at risk,” and that his party was “not in the business of wrecking the bill at all.”

Mr Bryant added that he hoped Labour’s proposed consultation would be “swift”.

Three Tory MPs – Tim Loughton, Charlotte Leslie and Rob Wilson – are pushing for civil partnerships to be an option for heterosexual couples as part of an amendment to the Marriage (Same Sex Couples) Bill.

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

David Cameron’s official spokesman said the prime minister was expected to vote against Tim Loughton’s amendment, but declined to say whether defeat would scupper the bill.

Earlier, Liberal Democrat leader and Deputy Prime Minister Nick Clegg 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.”

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

Mrs Miller has tabled a second amendment, which would mean a review for civil partnerships for straight couples, five years after the introduction of equal marriage.

Shadow Home Secretary and Minister for Women and Equalities Yvette Cooper told SkyNews: “We are trying to rescue the bill from the mess it seems to be getting into now, everything seems to be getting sucked into this vortex of Tory infighting.

“We in the Labour Party strongly support the equal marriage bill. We want people to be able to get married regardless of their gender and sexuality.”

Some Tory MPs have told PinkNews.co.uk that they will vote in favour of the Labour amendment, rather than the amendment tabled by Tim Loughton.

Ministers warn that straight civil partnerships would introduce significant delays to the introduction of same-sex marriage and impose additional costs of as much as £4bn.