Gay marriage is now supported by 62% of British voters with only 31% opposed – boosting government plans to legalize it next year.

The UK government is pressing ahead with legislation to introduce equal marriage in England and Wales and a separate bill will do the same job in the Scottish Parliament in 2013.

The poll showing overwhelming support for the changes comes after a Christmas marked by attacks on same-sex marriage.

The Bishop of Shrewsbury Mark Davies compared those pushing for gay marriage to Communists and Nazis. And his boss, the Archbishop of Westminster, Vincent Nichols, who is Britain’s most senior Catholic branded the government’s plan for equality ‘shambolic’.

The new poll will be a blow for Nichols who said the government had no mandate for same-sex marriage, falsely claiming it did not appear in manifesto documents at the time of the last election.

The poll, released today, was conducted by ICM for the Guardian with a sample of 1,002 British voters just before Christmas.

It showed 62% support the gay marriage proposals, only 31% oppose them and 7% are undecided.

That’s up sharply since an ICM online survey for the Sunday Telegraph in March which showed only 45% support. The new poll is closer to previous unbiased surveys.

The Guardian/ICM research also showed support across the political spectrum. Of those who voted Labour in 2010, 67% support marriage equality. And voters for the two government parties in that year’s general election also back it – 71% of Liberal Democrat voters and 52% of Conservative supporters.

The poll also shows support from 65% of women and 58% of men. All social classes back gay marriage though only 51% of those in the lowest occupational grades do so, 68% in the top professions are in favor.

And there is solid support in all of the UK’s nations, although the Welsh are most enthusiastic with a 74% majority.

Over 65s are the only age group to resist marriage equality, 58% are against with only 37% in favor. But it has 64% backing from 35 to 64-year-olds, 75% among 25s to 34s and huge support from 18s to 24s, 77% of whom are in favor.

Both Conservative Prime Minister David Cameron and his Liberal Democrat deputy, Nick Clegg back gay marriage and the Guardian says this poll will ‘encourage’ them showing ‘they are on the right side of history’.