Sir John Major has thrown his support behind same-sex marriages in churches and says David Cameron’s backing of the reform is “genuine”.

The former prime minister has released a statement through Freedom to Marry, a newly formed group of senior Conservatives in favour of allowing religious organisations the option to offer marriages for gay couples.

“The prime minister’s instinct to support equal marriage is a courageous and genuine attempt to offer security and comfort to people who – at present – may be together, yet feel apart,” said Sir John.

“I fully understand that there are many who will find this difficult to accept, as will the churches.

“But the prime minister has made it clear that the churches will be free to make their own decisions upon whether to conduct such marriages – and that is entirely the right approach.”

Sir John, 69, added: “We live in the 21st century and must move on: every couple should have the opportunity and the right to formalise their relationship.”

Members of Freedom to Marry include Education Secretary Michael Gove, London Mayor Boris Johnson, Transport Secretary Patrick McLoughlin, former defence minister Nicholas Soames, and the influential editor of the ConservativeHome website Tim Montgomerie.

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.

David Cameron has promised a change in the law in England and Wales by the next election in May 2015.

Speaking in favour of equal marriage on Friday, Mr Cameron said he did not want gay couples to be excluded from a “great institution”.

However, more than 100 of his MPs are thought to be against the idea.