In a letter sent to peers ahead of next week’s House of Lords Second Reading of the Marriage (same sex couples) Bill, a group of MPs have accused party Whips of threatening the careers of MPs opposed to equal marriage, despite there being a free vote on the Bill in the House of Commons.

The letter published by Guido Fawkes, was sent to peers by fifteen MPs from mainly the Conservative Party, but includes two members from the DUP, and one Labour Co-Operative member.

It accuses the Bill of being “deeply flawed”, and “unpopular”, and claims that MPs were not allowed to oppose it, despite the three major parties allowing a free vote on it.

The letter reads: “Regrettably, our ability as MPs to oppose, amend or scrutinise this Bill was heavily constrained. At Second Reading, backbench speeches were limited to only 4 minutes. The main parties announced a free vote but we saw varying degrees of coercion, with threats made, for example, to an MP’s future political career or withdrawal of party support at future elections.”

The letter goes on to claim that by having a Commons Committee of 19 MPs, was unfair, in favour of having a Whole House Committee, claims that the debates were limited to five days, compared to other bills which had longer periods of debate.

It also claims the Committee was stacked in favour of the Bill, and notes that the Government accepted no amendments to it.

“The Government presses on without any mandate from a party manifesto. We are all elected representatives but none of use was elected on a platform to redefine marriage… The consultation exercise was always about ‘how’ to introduce the changes, not whether to do so.”

It then claims that “most of” the constituents of the included MPs “believe marriage is a unique institution that forms the bedrock of society and should therefore be left as it is”, referring to the “deep unpopularity” of the Bill, which it calls “deeply flawed”.

The Bill is signed by Tories: MP for South East Cambridgeshire Jim Paice , MP for Gainsborough in Lincolnshire Edward Leigh, MP for Montgomeryshire Glyn Davies, MP for Congleton Fiona Bruce, MP for South Dorset Richard Drax,  Karl McCartney, MP for Peterborough Stewart Jackson, MP for Suffolk Coastal Therese Coffey, MP for Aldershot Gerald Howarth, and MP for Calder Valley Craig Whittaker.

The letter was also signed by DUP member Jim Shannon, MP for Upper Bann David Simpson, as well as Labour Co-Operateive MP for Heywood and Middleton Jim Dobbin,

Also signing the letter was Tory MP for East Worthing and Shoreham Tim Loughton, who had proposed what became known as a “wrecking amendment”, to allow civil partnerships to opposite-sex couples. The amendment was not accepted.

The Conservative MP for Enfield-Southgate David Burrowes, who also signed the letter, last week reiterated his opposition to the same-sex marriage bill, but also stated that he was opposed to Mr Loughton’s amendment.