On Tuesday more Tory MPs voted against gay marriage than in favour, leaving a question mark over how successful David Cameron's modernisation project has been and how long it will last after he departs.

The prime minister has insisted he wants to remain Tory leader and prime minister until 2020, but if he goes, or is toppled sooner, five names are repeatedly mentioned as candidates - some more seriously than others - Boris Johnson, Michael Gove, Jesse Norman, Theresa May and Adam Afriyie.

Johnson was unable to vote on the Bill as he is not an MP – at the moment. The mayor of London is widely seen as the main challenger to Cameron for the top job in the party. Many expect him to make a return to parliament in time for, or just after, the 2015 general election.

Following the vote, Johnson said: “You can’t champion equality in a free society if people aren’t truly equal.

“The passage of this Bill is an important step on the road to redressing that inequality, and I welcome tonight’s vote.

Michael Gove, often seen as the most likely member of the current cabinet to have a go at succeeding Cameron, was a vocal backer of the plans and supported the Freedom to Marry pro-gay marriage group. He also voted in favour of the Bill.

However his confidence in the legislation was slightly undermined on the eve of the vote when the chair of his local party claimed Gove told him there was a risk Churches could be forced to conduct gay weddings.

Home secretary Theresa May is also often spoken of as a sucessor to Cameron. May has, so far, avoided being eaten up by the Home Office brief and, aside from a bit of trouble with the UK Border Agency, has avoided getting into any major trouble.

May, who famously (to the fury of many Tories), told her party it had to stop being the "nasty party", voted in favour of gay marriage.

In fact, on the eve of the vote, May signed a joint letter with William Hague an George Osborne urging her fellow MPs to back the Bill.

"Civil partnerships for gay couples were a great step forward, but the question now is whether it is any longer acceptable to exclude people from marriage simply because they love someone of the same sex," she said.

Jesse Norman, the Hereford and South Herefordshire MP who led the Tory rebels against Lords reform, kept his options open by not voting.

In an interview with the New Statesman in October last year, one of the stars of the 2010 intake acknowledged he had not expressed a public view on gay marriage. "I’ll look at the bill and decide," he said at the time.

Following the vote, Norman rejected the suggestion his absence was based on leadership calculations. "Actually Tim," he said on Twitter in response to a jibe from the Daily Mail’s Tim Shipman, "it screams someone who's tried to think hard about it and thinks there are good Tory arguments on both sides."

Adam Afriyie, the Windsor MP at the centre of a recent alleged plot against the prime minister voted to block gay marriage. However, the little-known backbencher's nascent leadership bid may have been fatally damaged after it was exposed in its infancy.

None of the four spoke during the debate.

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