Westminster will not make decisions on governing Northern Ireland without consent from the Irish government, a former Alliance Party leader has said.

Lord John Alderdice told the Northern Ireland Affairs Committee that he believed direct rule from Westminster would not happen and so a form of joint authority between the British and Irish governments could emerge from a lack of devolution.

Former first minister Baroness Arlene Foster, who was also giving evidence to the Commons committee, said that the Good Friday Agreement did not allow for such a political arrangement.

The powersharing institutions at Stormont have not been operational for over a year due to the DUP’s boycott in protest against post-Brexit trading arrangements.

If there is no effective devolution, then things devolve upwards to the two governments to operate

Lord Alderdice referred to the three strands of the Good Friday Agreement established to encourage political co-operation within Northern Ireland, Britain and the Republic of Ireland.

Strand one refers to the powersharing Assembly and Executive, strand two refers to the North/South institutions and strand three refers to East/West institutions, notably the British/Irish Intergovernmental Conference.

Lord Alderdice said in the absence of a devolved government at Stormont, then Northern Ireland would begin to be operated jointly by the British and Irish governments.

“There are three strands to the agreement, there are three sets of institutions. If strand one in the assembly is not operational, strand two cannot be operational, but strand three does not depend on the Northern Ireland parties, it’s the British and Irish governments in the intergovernmental conference,” he said.

“And if there is no effective devolution, then things devolve upwards to the two governments to operate.

“And the point that I have been making is that, there is no way that the British government for example, in the absence of assembly, is simply going to go back to old-style direct rule.

“It’s just not going to happen politically, it’s not going to happen.

“And therefore you move into a situation where the British government will not operate things in Northern Ireland without consultation with the Irish government.”

Lord Alderdice also said that the British and Irish governments had not been fulfilling their responsibilities to Northern Ireland, as outlined in the Good Friday Agreement, citing that the British Irish Intergovernmental Conference did not meet between 2007 and 2018.

“It didn’t happen. And it didn’t happen because the two governments were not fulfilling their responsibilities under the Good Friday Agreement,” he said.

He added: “They weren’t meeting, they weren’t doing their job. So apart from the historic role of being the engine that drove the whole process, way, way back into the ’70s, they were also governments that had their own responsibilities they signed up for under the Good Friday Agreement and they didn’t fulfil them.”

Lady Foster said that joint authority would not happen as the intergovernmental conference did not have powers to legislate in Northern Ireland.

“Just to take up on the intergovernmental conference, it’s not an executive body. To John’s point about joint authority, it is only a consultative body, they don’t take decisions,” she said.

“The UK government take decisions in relation to Northern Ireland, not the Republic of Ireland.”

Under the Belfast Agreement it is very clear, the constitutional position of Northern Ireland is spelled out, unless and until there's a majority that decides if they want to go in a different direction

Dame Arlene further stated that joint authority had no place in the Belfast/Good Friday Agreement.

“The reason why the Belfast Agreement was able to be sold to a proportion of unionism was because the constitutional position was spelled out very clearly in the Belfast Agreement,” she said.

“And I know John has made some comments recently about joint authority. I mean, there is no space for joint authority in the Belfast Agreement. It’s not there. If John’s advocating moving away from the Belfast Agreement towards that position, then that’s a different scenario.

“But under the Belfast Agreement it is very clear, the constitutional position of Northern Ireland is spelled out, unless and until there’s a majority that decides if they want to go in a different direction.”

While speaking to MPs on the committee, Lord Alderdice said unionism was “no longer a dominant majority” in Northern Ireland.

In last month’s council elections, Sinn Fein overtook the DUP to become the largest party in local government, after also overtaking the DUP at last year’s assembly election for the first time.

Dame Arlene, a former DUP leader, said that unionism represented a diversity of opinion.

“In terms of unionism I think John (Alderdice) is trying to portray unionism as a very traditional force, there’s very many progressive unionists, I mean unionism is not a monolith,” she said.

I'm not at all surprised that unionists were unhappy about what I said, but what I was trying to do was point out what I perceive to be the reality of a trajectory, which is continuing and will continue

She added: “There are many different reasons why unionists are unionists, culturally, politically, socially, economically, whatever, and it’s not right to say that we’re all just traditional in our bunkers.

“I think it is the case that many of us want to remain within the United Kingdom because it is the United Kingdom of today, and that’s just the reality.”

Lord Alderdice stated that he was not surprised that unionists were upset with his comments on joint authority and on changes in Northern Ireland’s political landscape.

“I’m not at all surprised that unionists were unhappy about what I said, but what I was trying to do was point out what I perceive to be the reality of a trajectory, which is continuing and will continue,” he said.

“Arlene (Foster) quite rightly identified a series of things which were – to put it at the lowest level – upsetting to unionists, things that had happened, which were offensive in some cases and deeply disturbing.

“But we also have to remember that, in terms of the way people who are not from the unionist tradition, and not just nationalists, look at things they say, well, wait a minute – the DUP walked out of the talks that led to the Belfast Agreement, they never supported the Belfast Agreement.

“And of course, they did support Brexit, which was deeply offensive to many Northern Ireland people who wanted to remain part of the United Kingdom.

“So the truth is that each side has found itself doing things that have disturbed.”