The [UK] Government will hold a consultation on redefining marriage in England and Wales to allow homosexuals to wed, following similar moves in Scotland.
The announcement was made at the weekend by equalities minister Lynne Featherstone.
Opponents say there will be far-reaching consequences if a key social institution is so radically rewritten.
The consultation will begin in the spring. The Government says it will ask how, not if, same-sex marriage should be legalised.
Downing Street sources claim David Cameron’s personal intervention has pushed the issue forward.
Mike Judge, of the Christian Institute, questioned the need to redefine marriage to include unions between homosexuals.
"All the legal rights of marriage are already available to homosexual couples through civil partnership registrations," he said.
"The census shows that only one household in 500 is headed by a same-sex couple.
"Is marriage to be redefined across the whole of society to please a small minority of activists?"
The Prime Minister has reportedly personally intervened to speed up progress on allowing homosexuals to marry.