Change is a slow process. People usually need time to adjust to evolving social norms, especially when it comes sex - a subject we Brits struggle to discuss without giggling.

But sometimes history picks up the pace a little, pushing the unspoken and unresolved into the open. The year gone by was full of noticeable steps forward for LGBT campaigners on both sides of the Atlantic, and 2013 promises more big moments. Current momentum suggests gay marriage could become one of the defining issues of both the Obama presidency and Cameron government.

Here in Britain, the prime minister has promised to press ahead with plans to legalise same sex marriage. Last spring a Populus poll found 65% of people agreed "gay couples should have an equal right to get married, not just to have civil partnerships." Boris Johnson wants the government to "whack it through" and former prime minister John Major wants the Tories to "move on" by permitting gay couples to wed.

The political climate has changed considerably since the early 1950s, when only a few brave MPs urged Churchill's Conservative government to review Britain's sex laws following a flurry of arrests for homosexual offences (the actor Sir John Gielgud was fined for "persistent importuning" in west London).

Very few today would welcome a return to the days when homosexuality was the 'disease' that dare not speak its name. In much of Britain today, same-sex relationships are fast-becoming a matter of shoulder-shrugging ordinariness.

Attitudes in America are also changing quickly. Politicians (even those on the right) can sense the turning tide. April saw president Obama's landmark announcement in support of gay marriage, and last month Newt Gingrich told The Huffington Post of his evolving position. "It is in every community. The momentum is clearly now in the direction in finding some way to... accommodate and deal with reality."

The last days of the year saw the first gay wedding ceremonies in Maine, one of the three states voting in favour of legalising gay marriage in November's referendums. Legislators in Illinois are now seeking to make the state the 10th to approve marriage between same-sex couples.

So if the politicians appear to be moving toward the enshrining of equality, what about our religious leaders?

Blessings are not forthcoming. In the UK, leaders of the Church of England and Church in Wales (as well as the Catholic Church) have made their opposition to the proposed bill on gay marriage clear, despite the fact that no church would be forced to hold a same-sex ceremony against its wishes. Some smaller groups, including the Quakers, Unitarians and Liberal Judaism are in favour and will be able to 'opt-in' to holding ceremonies.

Not all Anglicans are happy about the established church's dogmatic position, one so out of step with 21st century Britain. The Church of England, after all, prides itself on a quiet, unfussy kind of tolerance. In the 1950s the Church's Moral Welfare Council was a key influence on the Wolfenden Commission's recommendations to abolish the law forbidding male homosexual activity (it was eventually made legal in 1967).

One recent compromise - before Christmas the Church of England let gay men in civil partnerships become bishops if they also remained celibate - suggests the Church is still capable of adapting to the world around it, however awkward the accommodation. There is now speculation that a top-level panel of bishops is discussing whether gay couples be allowed to have civil partnerships blessed in church (if they agree to the quaint charade of celibacy). By such messy adjustments, there is at least the possibility of the past merging into the present.

In the United States, the evangelical movement's traditional discomfort with homosexuality is less monolithic than might be supposed. The enormous diversity in approach to worship has allowed many young 'mission' churches to forge a new kind of tolerance toward gay members of the congregation.

Prior to the 2012 presidential election I interviewed a group of young evangelicals (some keen Obama supporters) about some of the subtle changes taking place under the radar. On a host of hot-button issues, young Christians are thinking differently than their parents' generation, and a trend toward a more moderate stance on same-sex relationships is evident.

Tim, 25, Christian and gay, has struggled to find acceptance after moving from church to church in his home state of Kansas. He was keen to make clear the strong prejudice still making itself felt in places of worship: "The issue is just too big for many churches to concede at the moment, but there is less hostility than you might expect.

"The shift toward acceptance is a matter of exposure. Being around different kinds of people makes us more cosmopolitan than we mean to be, even in a place like Kansas. Norms change. On a lot of social issues, things are easier for me than someone in my parents' generation."

John Shore, an author and theologian who blogs regularly on the topic, believes attitudes among young people have created an "inevitability" about a shift toward tolerance. "Things that used to be formulated and reformulated on the gay issue in Christian circles over decades are now changing in a matter of months. The case (for equality) is so emotionally compelling that its writing is on the wall for the years ahead.

"What made it easier in the old days to condemn to hell a whole class of people was that they knew no one from that class. But now, with the internet, connections with all kinds of people are impossible to avoid. Even in the small Bible colleges it's difficult to maintain the old insularity."

So if secular society is moving away from discrimination on the basis of sexuality, it seems many Christians are also beginning a journey of their own in the same direction. If the Church of England insists on 'this far and no further', it might find itself cut adrift from the life of the nation, and from very many people of faith.

Follow Adam Forrest on Twitter: www.twitter.com/@adamtomforrest