Cameron faces Tory revolt over gay marriage David Cameron faces a mass revolt by Tory MPs on gay marriage next week, with ministers resigned to the fact that at least half the party's backbenchers will refuse to support the prime minister on the issue. The uprising reveals the gulf between the prime minister and some members of his party and will heighten speculation on a possible leadership challenge by disgruntled rightwingers before the 2015 election. The vote on Tuesday is expected to be carried with the support of Labour and Liberal Democrat MPs, but ministers expect no more than 40 per cent of Tory backbenchers will back Mr Cameron in what is officially a free vote on "a matter of conscience." In fact, the vote is a test of Mr Cameron's success in modernising his party. George Osborne, chancellor, has argued that gay marriage is a litmus test of its determination to stick to the political centre ground. Mr Cameron's offer of a referendum on Europe won him plaudits from the Tory right; but the cheers that greeted the prime minister in the Commons have been replaced by whispers of plots to replace him. Last weekend rumours, promptly denied, surfaced of a plan to install as leader Adam Afriyie, the 47-year- old multimillionaire MP for Windsor. Few Tory MPs expect a serious leadership challenge before the next election. Mr Cameron's aides say the prime minister has shrugged off reports. He feels things are going well. He's showing leadership on issues like Europe, fighting terrorism and the polls are looking up," said one. But Mr Cameron's defeat on Tuesday in a Commons vote to reform parliamentary boundaries - changes that might have given the Tories an extra 15-20 seats - has altered the mood at Westminster. "It seems almost impossible that we can win the next election, given we didn't win outright last time," said one MP, citing Mr Afriyie and other prominent backbenchers such as Graham Brady or Jesse Norman as potential leadership challengers. Under Tory rules a vote of confidence would be triggered automatically if 15 per cent of the parliamentary party, or 46 MPs, write to Mr Brady, chairman of the backbench 1922 Committee. The major block, however, is the lack of an obvious unifying candidate, with even "big beasts" such as David Davis or Liam Fox struggling to attract support from outside their own wings of the party. Mr Cameron's critics have a familiar list of grumbles: some believe he is elitist, others say he fails to listen to his party, others would like to be more robust on cutting taxes, Europe, or scrapping employment laws. But the prime minister's underlying problem is that he failed to win the last election against a politically crippled Gordon Brown and much of his party cannot see how he will do much better in 2015.