The relationship between the Dublin and British governments has improved “dramatically” in the past year but is still “not where it should be”, according to Taoiseach Leo Varadkar.

Mr Varadkar said that “Northern Ireland works best” when the two governments are “hand-in-hand”.

“That hasn’t been the case for a very long time now. We appreciate that the Irish government is not the sovereign government in Northern Ireland, we don’t claim to be… but we are co-guarantors of the Good Friday Agreement [Belfast Agreement] and we have a role to play,” he said in Belfast on Wednesday.

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As the North enters its 18th month without a functioning Executive, Mr Varadkar travelled to the city to meet leaders of the five main political parties amid efforts to break the deadlock.

The Democratic Unionist Party (DUP) is boycotting the powersharing institutions over its ongoing opposition to post-Brexit trading arrangements.

Mr Varadkar said he “remains hopeful” that Stormont will be restored by autumn. But he said that “alternatives” must be discussed if the political crisis continues.

“If it’s the case that the institutions can’t be re-established in the autumn, well, then I do think at that point we have to start having conversations about alternatives, about plan B,” he said. That’s very much a conversation that I’m keen to have with the UK government. I don’t want to speculate too much at the moment, because I still believe it is possible to get the institutions up and running in the autumn. I do think the suspension has gone on for a long time. There is drift. And that’s not good for Northern Ireland.”

Asked what those alternatives would be, he replied he did not want to discuss that.

[ Stormont restoration talks making progress, says Heaton-Harris Opens in new window ]

The development follows the Taoiseach’s criticism of the British government on Monday when he claimed it was reluctant to involve Dublin in work to end the North’s political stalemate. Asked about the current strain in relations despite more engagement with London in recent months, Mr Varadkar replied the “very close” relationship that once existed between the two governments was disrupted by Brexit.

“It wasn’t very good for a period of time but it has improved dramatically and immeasurably in the past year and we’ve seen the fruits of that, for example, the Windsor Framework,” he said.

Struck by London and Brussels earlier this year, the Windsor Framework pact sought to reduce the red tape on goods entering Northern Ireland from the rest of the UK while maintaining dual market access.

The DUP has insisted the deal does not go far enough to address its concerns around sovereignty and the application of EU law in Northern Ireland.

After her meeting with Mr Varadkar, Sinn Féin first minister designate Michelle O’Neill said “public patience is wearing thin” with the DUP. She said she agreed with the Taoiseach that the British and Irish governments need to be working together to revive the Executive.

“I’ve heard more urgency from the Taoiseach today than I’ve heard from the British government in terms of the need to restore the Executive,” she said.

DUP leader Jeffrey Donaldson said he spoke to Mr Varadkar about “matters of mutual interest and concern. Our focus at the moment is on resolving the major problems that were created by the Northern Ireland protocol. We continue to engage with the government, that engagement has intensified in recent weeks, and I hope that within the next few weeks, we will have a definitive response from the government and we’ll be able to put a proposition forward.”

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The DUP leader added that he wanted Stormont restored and “properly functioning. But I am very clear: we need a solution that works for Northern Ireland that resolves the problems created by the Northern Ireland protocol and that protects in law our ability to trade within the UK internal market with the rest of the United Kingdom.”

Alliance Party leader Naomi Long said she is concerned that the window to restore the powersharing institutions before a UK general election is closing.

“I remain very concerned that as time passes the crisis that faces our public services and public finances is deepening,” she said.

UUP leader Doug Beattie described his meeting with Mr Varadkar as a “neighbourly catch-up”.

SDLP MLA Matthew O’Toole said most people in Northern Ireland are “frustrated” with what he described as a lack of engagement by the DUP on devolution, which he claimed was “increasingly abetted by the British government. We need to see [a] resolution to this quickly because devolution could be moving past a point of no return.” — Additional reporting: PA