Tory strategists have held meetings with US lobbying experts ahead of a drive to try to win hesitant Conservative MPs around to supporting gay marriage.

David Cameron is concerned that his own backbenchers could sink his plan to change Britain’s marriage laws, if and when the issue comes to a vote in the Commons.

Although he has repeatedly tried to portray the case for same-sex marriage as a “conservative” cause, many of his MPs vocally disagree.