Labour MP Conor McGinn made a passionate case in the House of Commons for same-sex marriage to be extended to Northern Ireland.
The Government has faced repeated calls to introduce marriage equality in the region since power-sharing talks at Stormont broke down over a year ago.
Backbencher McGinn, who was born and raised in County Armagh, told MPs Theresa May has a “moral and political duty to act” in the absence of devolved government.
He presented a Bill in Parliament on Wednesday, which would compel May to act, and said: “The assembly being in cold storage should not mean that Northern Ireland remains a cold house for LGBT rights.
“The de-facto suspension of the devolved legislature doesn’t mean that equality for same sex couples can be suspended indefinitely, because rights delayed are rights denied.”
He later joined campaigners in delivering a petition to 10 Downing Street.
The letter had 42,000 signatories and was presented by Cara McCann and Amanda McGurk - a same-sex couple from Northern Ireland planning to marry on Valentine’s Day next year.
They hope it will be a marriage, rather than a civil partnership.
Northern Ireland is the only part of the UK where gay marriage is not legal, despite overwhelming public support and a majority of MLAs in the assembly for the policy.
He added same-sex marriage has broad support with the public in Ulster.
“Attitudes have changed in Northern Ireland and on the island of Ireland,” he said.
He went on to joke about conversations he had in a pub in South Armagh which proved to him that everyday people were comfortable with marriage equality.
McGinn said: “In a recent and, these days, rare visit, I chance to encounter one of these wise men - a gruff, agricultural, straightforward South Armagh man and he said to me, ‘young McGinn, I see you’re helping out the gays,’ and he said: ‘Sure I’m all for this gay marriage, they’re as entitled to be as miserable as the rest of us.’
“And another asked, ‘You see this equal marriage, will they be able to get equal divorce too.’
“Madam deputy speaker, my point is when they are making jokes about it, you know that it is accepted and part of the fabric of everyday life.
“The people understand this, it is the law that remains stuck in the past, because LGBT people are their friends, neighbours and relatives – and this is fundamentally about people and their rights.”
McGinn told the House it saddened him that he had married gay friends who lived in New York and elsewhere in the UK who, when they stepped off the plane in Northern Ireland, effectively saw their marriage become null and void.
“I was born and raised in Northern Ireland and I’m now proud to represent the English seat of St Helens,” he said. “People in my constituency, in London, in Edinburgh and Cardiff and Dublin have the right to marry the person they love, but this very same right is denied to people in the place I grew up.”
McGinn also talked about a friend called James, who felt hurt by the lack of LGBT rights in Northern Ireland.
“What might be more surprising is that when he was a young man in Northern Ireland in the 1970s, homosexuality was still illegal,” he said.
“Despite being decriminalised in the 1960s in Britain, it wasn’t until the 1980s that it became legal in Northern Ireland.
“James is a proud Ulster man and has spent much of his life working for peace and reconciliation in Northern Ireland, but I know as his friend that it cuts him to the quick that he had to leave home as a young man because he was gay, and the prohibition of gay marriage means that he still is not equal in the land of his birth.”
Earlier the same day, Theresa May told the Commons she considered the legalisation of same-sex marriage a devolved issue after being told she was “hiding behind the DUP”.
She was responding to a question from Labour MP Ged Killen, who said: “LGBT rights in Northern Ireland are in limbo.
“The assembly has already voted for equal marriage and public support for it is overwhelming. Will the PM stop hiding behind the DUP and will she take this opportunity to put on record her support for the Bill being put forward by [Conor McGinn.”
May, who switched position to support David Cameron’s same-sex marriage legislation during the coalition years, said the Government has “championed” marriage equality, but added legislation brought in by Labour meant it was a devolved matter.
“We hope that there will be in place soon a Northern Ireland executive that will be able to address these issues,” she said.