Lib Dem MP Alistair Carmichael, who is the party’s Chief Whip in the House of Commons, says the decision to offer a free vote on marriage equality for his MPs is based on Labour and the Conservatives doing the same.

Writing on the Liberal Democrat Voice website, Mr Carmichael said: “As I explained at Federal Conference in September I take as my starting point that as this is a government bill brought forward by a government minister in government time then votes will be whipped.

“That is, however, what lawyers would call a rebuttable presumption and the Conservative and Labour parties having declared this to be a free vote for their MPs it would be wrong for me not to take the views of my colleagues before making a decision for Liberal Democrat MPs”.

The Lib Dem Chief Whip went on to say: “Accordingly the parliamentary party discussed the issue at its weekly meeting last night (11 Dec). The view of my parliamentary colleagues that came up time and again was that they supported equal marriage and were keen to see it on the statute book. They wanted, in fact, not just to support the bill but to be seen to support it because they do and not because they have been told to”.

Mr Carmichael added: “Incidentally no MP who spoke in the discussion last night opposed the idea of equal marriage. That is not to say that a few of my colleagues do not have significant concerns about the proposal as I know that some do. I strongly suspect that any colleague who does harbour doubts would not have these doubts addressed just by the application of an instruction to the vote.”

Mr Carmichael stressed the only decision taken at the meeting was in relation to the equal marriage bill’s second reading vote – the broad principle of the bill – for all other votes the MP said the initial presumption of whipping still applies.

In an exclusive interview with PinkNews.co.uk on Tuesday, Liberal Democrat leader Nick Clegg signalled that his MPs would now be given a conscience vote by saying: “I’m not going to be illiberal in pushing through a liberal measure”.

In May, Mr Clegg criticised David Cameron for granting Conservative MPs a free on the issue – at a time when the government’s official position was that it was only looking at reforming civil marriage laws and not those concerning religious establishments.

Labour had previously indicated it would impose a three-line whip.

However, on Tuesday, Labour leader Ed Miliband confirmed that he would not seek to whip his backbench MPs over the issue.

The change in position by both Labour and the Lib Dems has been attributed to the government’s decision to incorporate religious ceremonies in its proposed equal marriage bill.

However, the Labour Party’s affiliated LGBT campaign group criticised the decision and in a statement said: “LGBT Labour firmly believes issues of equality are not matters of conscience but fundamental rights. We believe this position has the strong support of Labour members and activists who also share our disappointment.”