A poll of MPs shows that most voters who write to them about the plans to redefine marriage are opposed to the measure.
The poll also shows that eight out of ten MPs want the freedom to vote according to their conscience.
And only one in four MPs think the Government should redefine marriage “irrespective” of the public opposition in the official consultation on the issue.
The Government has vowed to press on, regardless of what the public may think in the consultation.
David Cameron has, though, promised a free vote for his Tory MPs including Tory Government ministers – a number of whom want to keep marriage as it is.
But it is understood Labour and Lib Dem MPs may be forced to vote for redefining marriage, whether they agree with the proposal or not.
The poll of 154 MPs was conducted by ComRes on behalf of the Coalition for Marriage, the group leading the campaign against redefining marriage.
Three quarters of MPs (74 per cent) said the balance of correspondence about gay marriage was “negative” and almost half (47 per cent) was “strongly negative”.
Overall, 80 per cent of MPs favour a free vote, which means they don’t want party leaders forcing them to vote in a particular way.
A free vote is supported by 94 per cent of Conservative MPs, 72 per cent of Labour MPs and 56 per cent of Lib Dem MPs.
Only a quarter of MPs think the Government should redefine marriage “irrespective” of the size of opposition in the public consultation.
Colin Hart of the Coalition for Marriage said: “This poll will make uncomfortable reading for David Cameron and Nick Clegg, who continue to want to force through these undemocratic proposals regardless of what those who elected them say.
“It shows a growing sense of unease at the way redefining marriage is being handled, not least how the concerns of ordinary people have been ignored.”