DAVID Cameron's determination to push ahead with legalising gay marriage could cost him votes at the next General Election, the latest poll suggests.

The ComRes online snapshot of 2000 adults on the eve of today's vote on the Marriage (Same Sex Couples) Bill showed 34% of people felt it made the Tories less appealing while only 15% said it made them more appealing.

However, the British public appears evenly split as to whether or not the Coalition is right to legislate for same-sex marriage with 42% saying it is and 40% saying it is not.

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After 20 present and past Conservative local party chairmen warned the Prime Minister at the weekend that the proposed change could harm Tory electoral prospects, more pressure was heaped on him when Justin Welby, as he was confirmed as the new Archbishop of Canterbury, said he stood by the previous criticism of the Coalition's legislative plans for gay marriage by bishops from the Church of England – often regarded as the Tory party at prayer.

In contrast, 50 senior Conservative activists yesterday warned the party risked alienating voters if it did not back same-sex marriage.

Today, a combination of Tory, Labour and Liberal Democrat MPs look set to give the bill its second reading.

Labour leader Ed Miliband said he would "proudly" vote in favour and would urge his MPs to join him in making "an important step forward in the fight for equality".

Yet the focus will be on the Conservative rebellion with reports suggesting as many as 120 Tories, including ministers, could rebel against the official Coalition line.

UK Government ministers yesterday took to the media to back the legislation.

Maria Miller, the Culture Secretary, made clear Conservative anger would not prevent the Coalition from pushing ahead with legislation. She said the proposed change was in line with the party's progressive past on issues such as slavery.

David Mundell, the Scotland Office Minister and the only Scottish Conservative MP, told The Herald he would support the bill.

"It's a matter of equality. I can't see there is any reason that would justify not supporting it," he said.