A number of senior Conservative politicians announced today that they had formed a new campaign group which supports the right of same-sex couples to marry, in an act of defiance against traditionalists within the party.

In a letter to the Telegraph, a group of 19 senior Conservatives, which uses the slogan “Freedom to Marry”, includes Boris Johnson, London Mayor, and Michael Gove, the Education Secretary.

The Transport Secretary, Patrick McLoughlin, a Catholic, and who had previously been seen as a voice against equal marriage rights, also appears on the list in support of equal marriage.

The group was formed by Nick Herbert, the former Police Minister, and current Conservative MP for Arundel & South Downs. He resigned from the government in September following David Cameron’s first major reshuffle.

The letter from the senior Tories stated: “Marriage should be open to all, regardless of sexuality.

“We recognise that civil partnerships were an important step forward in giving legal recognition to same sex couples. But civil partnerships are not marriages, which express a particular and universally understood commitment.”

The issue of same-sex marriage has been divisive among Conservative politicians, with around 130 MPs appearing to be planning to vote against the measure when it comes before parliament in spring.

Some Conservatives have been vocal about their stance on the matter. Stewart Jackson, the Conservative MP for Peterborough and a member of the Public Accounts Committee, tweeted:

“Gay marriage bill will be massacred in the Lords and govt can’t use Parliament Act as it wasn’t in manifesto. Arrogant Cameron knows best.”

Conservative MPs will be allowed a free vote on the issue, and it is thought that a number of the party’s Cabinet Ministers will vote against it.

As well as Boris Johnson, and cabinet ministers, the letter includes signatures from Alistair Burt, the Foreign Office minister, an evangelical Christian, two other former Conservative ministers – Lord Fowler, and Nicholas Soames – and openly gay, Ruth Davidson, who leads the Scottish Conservatives.

Conservative Party activist, and columnist, Tim Montgomerie, and political blogger, and LBC host, Iain Dale are also signatories.

Reports suggest that the coalition government had hoped to introduce legislation legalising same-sex marriage “before Easter”, and the law would be expected to come into effect a year after that, with the first marriage ceremonies taking place in spring 2014.

In a comment piece published today, Nick Herbert, who is in a civil partnership himself, said today that legalising same-sex marriage is “the right the thing to do.”

He went on to point out that both Boris Johnson, and Barack Obama went on to win elections after lending their support to equal marriage.

Mr Herbert said: “It is precisely because marriage is such a uniquely important institution that we should ensure that all couples who want to enter into it, regardless of their sexuality, can do so.

“Conservatives who believe in marriage should feel this most strongly.”

He did go on to say that he thinks “safeguards” should be written into the legislation, because it would be wrong to “compel religious organisations to marry same-sex couples against their will”.

Both Boris Johnson, and Nick Herbert previously featured in videos for Out4Marriage announcing that they were in support of equal marriage rights for same-sex couples.

Out4Marriage said: “We’re glad that there is now a serious effort by Conservatives to campaign for equal marriage. The success or failure of this legislation is likely to fall on the hands of Tory MPs and Peers. Strong advocates from within the Parliamentary party is desperately needed to ensure that their colleagues vote for freedom and liberty for all in our country regardless of sexual orientation.”

On Friday, David Cameron confirmed reports that he is to back same-sex marriages for religious institutions, and he had previously promised that the law would be in place by the next election in 2015.

In late November, the Prime Minister revealed that he was intended to fast-track legislation to introduce equal marriage within weeks.

As well as Stewart Jackson, Tory MP Mark Pritchard said he feared exemptions for places of worship were likely to be ruled unlawful by the Supreme Court or the ECHR despite government assurances it would not be.

“Same-sex marriage Bill now exercises Tory grassroots as much as lack of progress on a referendum. Number 10 should hear the alarms bells,” he said on Twitter.

The Bishops’ Conference, representing the Catholic Church in England and Wales reaffirmed its opposition to the government’s move towards marriage equality. It said: “We remain firmly opposed to the Government’s proposal to redefine marriage.

“At this time, we urge all who oppose the government’s proposal to make their views known to their own member of parliament.

“What is at stake is the intrinsic meaning of marriage and what is best for society as a whole.

“Redefining marriage is therefore a fundamental moral issue which concerns everyone. It is also one for which no mandate was sought or given to any party at the last general election.

“It should therefore be treated as an issue of conscience, and we urge all parties to offer a free vote to their members if a bill ever comes to Parliament.”