A survey conducted in America this month has revealed support for same-sex marriage has grown to be a “mirror image” of ten years ago, with the majority now in favour of legalisation and many calling for a nationwide law.

The poll, conducted by the Washington Post and ABC News, found that 58% of Americans now support the legalisation of same-sex marriage, while 36% oppose it.

The Washington Post’s Jon Cohen says: “Public attitudes toward gay marriage are a mirror image of what they were a decade ago: in 2003, 37 percent favored gay nuptials, and 55 percent opposed them.”

The poll also revealed that the majority, 64%, felt that whether same-sex marriage is legal or not should be decided on the basis of the US Constitution rather than by individual states.

This is significant as next week the Supreme Court will begin hearings on the Defense of Marriage Act and Proposition 8, which could potentially lift bans on same-sex marriage or even result in the Court saying they are unconstitutional.

Other findings in the poll included a difference in support among age groups, with nearly seven in ten over-65s opposing same-sex marriage. That figure has dropped from over eight in ten in 2009.

Young people are more likely to support same-sex marriage, with the majority of both Democratic and Republican-leaning voters aged 18-49 polling that they were pro-equality.

The growing support for same-sex marriage reflects wider public opinion that being gay is not a choice. 62% of Americans now believe it is “just the way some people are”, while 20 years ago fewer than half did.

Around 75% of those who believed being gay was not a matter of choice “strongly” supported same-sex marriage, with a similar number, around two thirds, who thought it was a choice “strongly” opposed to same-sex marriage.

The poll was conducted on 7-10 March among a sample of 1,001 adults, with a 3.5% margin of error.

This week a poll by an American Christian group found that 64% of respondents agreed that “it is inevitable that same-sex marriage will become legal throughout the United States,” while 80% disagree that employers should be allowed to discriminate based on sexual preference.

A poll of American Catholics this month revealed a similar growth of support, with 54% percent in favour of same-sex marriage, and 52% saying Church leaders were out of touch on gay rights.