Tories warn PM that he's splitting his party over gay marriage, as leadership speculation mounts

David Cameron has been warned that his backing for gay marriage is splitting the Conservatives and that he has underestimated the strong opposition to it in his own party.

A survey of more than 2,500 Conservative Party members for The Independent found that a huge majority reject his arguments for legalising same-sex marriage.

The findings come amid renewed speculation among some Tory MPs that Mr Cameron could face a leadership challenge before the next general election. His critics fear that the UK Independence Party will exploit the opposition to gay marriage among natural Conservative supporters. They claim he will alienate Tory MPs further and if he fails to offer an "in or out" referendum on Britain's EU membership in a speech in the new year.

"Gay marriage is a toxic mix," one Tory MP said. "We are in danger of playing into Ukip's hands." Cameron allies dismiss leadership speculation as coming from long-standing critics.

The poll, carried out by the ConservativeHome website, found that seven out of 10 Tory members (71 per cent) believe that same-sex marriage is splitting the party and that three out of four (78 per cent) believe the Prime Minister has underestimated the strength of feeling.

Although Mr Cameron's standing among gay people has improved, according to another survey this week, most Tory members are unimpressed. Some 62 per cent believe he should worry more about traditional Tory supporters like church-goers and less about winning over others such as gay rights campaigners.

A majority of Tory members (64 per cent) think gay marriage is unnecessary because gay people can already opt for civil partnerships, while 32 per cent disagree. Almost six out of 10 (58 per cent) believe that marriage "should remain between one man and one woman", while 34 per cent disagree.

Only 38 per cent agree with the proposition that "marriage is an institution that brings two people together and there is no reason why two people should not be two men, two women or a man and a woman," while 58 per cent disagree. Mr Cameron's concessions to his Tory critics – including the proposal to make gay marriage illegal in the Church of England – appear to cut little ice. A minority (43 per cent) agree with the statement that they would not object to same-sex marriage as along as religious liberty is protected, while 51 per cent disagree.

Only one in three Conservative members (36 per cent) admires Mr Cameron for "standing up for gay equality", while 55 per cent do not.Seven out of 10 (71 per cent) think same-sex marriage will not be a "big issue" at the next election.

Some 2,568 Torys took part in the survey between 22 and 26 December.