Just two of eleven Conservative MPs in Devon and Cornwall last night fully backed gay marriage proposals on the eve of the first parliamentary vote on the reforms.
David Cameron has personally championed allowing same-sex couples to get married in both civil and religious ceremonies, where a religious institution has formally consented.
But the Prime Minister will face resistance from MPs claiming the proposals de-value the institution of marriage during a free vote at the second reading of the Bill today. A free vote, which applies when MPs are asked to vote on an issue of conscience, allows MPs to break free of the party line.
Devon and Cornwall MPs that last night indicated they would vote against the Bill were Anne Marie Morris (Con, Newton Abbot), Neil Parish (Con, Tiverton and Honiton) and Mel Stride (Con, Central Devon).
Mr Parish said: "These things are best left to evolve. This should be for the church and Christians to decide not for Parliament to legislate."
Gary Streeter, Tory MP for South West Devon, is understood to be against the Bill, as it was not in the party manifesto, but he is chairing it through committee stages and so cannot give a public view or vote on it at any stage.
Other Conservatives signalled they were undecided. Tory MP for Plymouth Sutton and Devonport, Oliver Colvile, said he wanted to inform constituents first.
Geoffrey Cox, Conservative MP for West Devon and Torridge, said he was "pretty confident" that he knew which way he was going to vote but "will keep my mind open at the debate".
Sarah Newton, Conservative MP for Truro and Falmouth, is in favour of the reforms but has indicated she will vote with the majority of her constituents by the time of the final Commons vote.
South East Cornwall Tory MP Sheryll Murray is taking soundings from constituents before the third and last reading of the Bill.
George Eustice, Conservative MP for Camborne and Redruth, said he is likely to abstain, arguing civil partnerships are "working well".
Hugo Swire, MP for East Devon and Foreign Office Minister, and Totnes MP Sarah Wollaston were the only Conservatives in the region to firmly back the plans.
Dr Wollaston said her postbag indicated opposition to the reform was based on "prejudice that needs to be confronted": "I think there will be a lot of MPs who will be proved to be on the wrong side of the argument."
Liberal Democrat MPs Stephen Gilbert (St Austell and Newquay), Nick Harvey (North Devon), Dan Rogerson (North Cornwall) and Adrian Sanders (Torbay) will all back the Bill, they said last night.
Andrew George (Lib Dem, St Ives) said he will decide after today's debate – though is "presently minded to vote for the Bill".
Labour MPs Ben Bradshaw (Exeter) and Alison Seabeck (Plymouth Moor View) also support the legislation.