Opponents of gay marriage warned of a “long, protracted battle” ahead as they prepare for a last-ditch attempt by peers to scupper the plans.
The proposals move to the Lords next month after being approved by MPs by a large majority despite the opposition of 130 Tories.
Sixty-five peers have already signed up to speak on the Marriage (Same Sex Couples) when it receives its second reading in the Lords on June 3 and many more are expected to follow suit.
The number, and the fact the Government has only allocated one debate to the subject, means the debate is set to drag on into the small hours. That raises the possibility of opponents attempting an ambush when the Lords is thinly-populated.
Lord Tebbit, the former Tory chairman and an outspoken critic of the plans, is among several ex-ministers who have applied to speak.
The Coalition for Marriage, which is leading resistance to the Marriage (Same Sex Couples) Bill, accused David Cameron of being a “marriage wrecker”.
Colin Hart, its campaign director, said: “If he thinks he got a rough ride in the Commons, just wait for the Lords. It will be a long, protracted battle which will only remind the voters that the Government isn’t listening.”
Mr Cameron insisted he was proud of the legislation but, in an apparent olive branch to traditionalist Tories, the Prime Minister promised there would be no more legislation on sensitive social issues.
He said: “There will be young boys in schools today who are gay, who are worried about being bullied, who are worried about what society thinks of them, who can see that the highest parliament in the land has said that their love is worth the same as anybody else's love and that we believe in equality.
“I think they will stand that bit taller today and I’m proud of the fact that has happened.”
But he made clear he was not planning further initiatives on equality issues.
“If you are saying to me, ‘Is this the first of many other issues like that?’, no it isn't,” he said.