Members of Parliament last night overwhelmingly endorsed historic legislation that will give gay couples the equal right to marry – although it was backed by only two of Northern Ireland's MPs.
But the Tory rebellion was larger than expected with 136 taking advantage of a free vote to register opposition. Just 127 endorsed the proposals at second reading, with 40 more either formally abstaining or not voting. There were 75 abstentions.
SDLP leader Alasdair McDonnell and South Down MP Margaret Ritchie were not present for the vote. A party spokesman said Mr McDonnell had other commitments, while Ms Ritchie had suffered a family bereavement.
Westminster's plans for same sex marriage will not apply to Northern Ireland. It falls under the responsibility of the Finance Department, led by the DUP's Sammy Wilson, an opponent of same sex marriage.
DUP opposition runs so high that when some loyalist flag protesters urged a return to direct rule, First Minister Peter Robinson used the legalisation of gay marriage by Westminster as a reason to back the Assembly.
Nick Clegg hailed the vote as a "landmark for equality in Britain" which showed "no matter who you are and who you love, we are all equal", while Ed Miliband said it was "an important step forward in the fight for equality".
But seven hours of intense and often heartfelt debate revealed deep divisions on both sides of the House over the proposals. Dozens of Conservatives, including a cabinet minister, defied the appeals of David Cameron to vote against changing the law, claiming it would impinge upon religious freedoms.
To the dismay of gay marriage supporters, neither David Cameron nor the string of senior Conservative ministers who have recently come out to back the change sat in the Commons as the Culture Secretary Maria Miller outlined the Government's plans.
In recent days Mr Cameron has also declined to reiterate his public support for the Bill with Downing Street insisting it was a free vote.
However, an hour before the vote he recorded a last-minute television interview saying the move would make society stronger.
"As a Christian and a liberal, I believe that equality and religious freedom are fundamental to a democratic society and that both must be promoted and protected, a position which is reflected in our policy and also in the Bill. I, therefore, supported the Bill."
East Belfast MP Naomi Long
We're mired in a mass of legal confusion
By Liam Clarke
Westminster's move to legalise same sex marriage looks set to open the floodgates for a series of test cases in Northern Ireland – unless Stormont comes into line with the law in Britain.
As fundamental gaps open up between family law here and in Britain, gay couples in Northern Ireland will now travel to England to get married and adopt children – just as pregnant women travel to Britain for abortions.
It is already legal for gay couples in civil partnerships in England and Wales to adopt children. But in Northern Ireland, only couples who are married are allowed to do so – although single people living on their own are eligible to adopt.
Adoptions carried out abroad are generally recognised by Northern Ireland's courts, but what will happen when they involve same sex partners is not clear.
Adding to the legal confusion, same sex marriages carried out in England will only count as civil partnerships in Northern Ireland.
Last October, Assembly Members rejected a motion to introduce same sex marriage here. The growing differences between Northern Ireland's devolved laws and more liberal laws in other parts of the UK is creating a legal minefield.
Professor Michael O'Flaherty (right), Chief Commissioner of the Northern Ireland Human Rights Commission, said there is no explicit right to same sex marriage in international human rights treaties. However, he added: "Extending the right to marry, which is protected by the Human Rights Act, to same sex couples in England and Wales may raise issues regarding the equal protection of human rights in Northern Ireland.
"We have raised this issue with the Department of Finance and Personnel in Northern Ireland as well as with Westminster."
Professor O'Flaherty warned that disputes over child custody and inheritance rights may "engage such human rights concerns as the right to family life, the best interests of the child, property rights and discriminatory access to justice".
The NIHRC has already won a ruling permitting adoption for same sex couples but it is currently being appealed by the Department of Health.
Alliance, the SDLP, Sinn Fein and the Greens supported same sex marriage in last year's Assembly vote. The UUP offered its members a free vote, while a DUP-led majority opposed it.
The DUP tabled a petition of concern – ironically, a device originally drawn up to protect minorities – which would have given it a veto had they needed it. Gavin Boyd, of gay advocacy group the Rainbow Project, predicted that "a legal morass will ensue if people are recognised as legally married in one part of the UK but not the other".
The Republic is also reviewing the laws on same sex marriage, with most parties favouring change over the border.