The UK does not rule out the possibility of invoking Article 16 of the Northern Ireland Protocol if a trade disagreement with the European Union cannot be resolved, Prime Minister Boris Johnson has said.

The protocol is an arrangement aimed at protecting trade between Britain and Northern Ireland and preventing the return of a hard border in Ireland.

"The protocol is not working in the way that it needs to in order to guarantee the Belfast Good Friday Agreement," Mr Johnson told the House of Commons in London.

Invoking Article 16 would not axe the protocol, but rather instigate another negotiation process over its operation.

Mr Johnson's remarks - in response to a question from DUP leader Jeffrey Donaldson - come as UK and EU officials continue technical discussions aimed at finding solutions to issues created by the economic border in the Irish Sea.

Both sides are trying to reach agreement that would reduce customs paperwork and the numbers of checks required on goods moving from Britain to Northern Ireland and ensure a continued free flow of medicines across the Irish Sea.

While the UK also wants to see the removal of a protocol oversight role for the European Court of Justice, the EU has refused to countenance such a move.

The UK government has repeatedly warned that it will trigger Article 16 if progress is not made.

However, there is mounting concern among some unionists in Northern Ireland that Mr Johnson has yet to follow through with that threat.

Unionists and loyalists are strongly opposed to the protocol, arguing it has altered the constitutional position of Northern Ireland in the UK without their consent.

They claim it has undermined the principle of consent that was the fulcrum of the Good Friday Agreement.

Nationalist and non-unionist parties in Northern Ireland take a different view.

While they concede that operational issues with the protocol need to be addressed, they insist the arrangements can actually be beneficial for the region in the long term.

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Mr Donaldson, who has threatened to collapse the power-sharing institutions at Stormont if major changes to the protocol are not secured, raised the issue again today.

He asked: "In view of the harm caused to political stability in Northern Ireland and to our economy by the Northern Ireland Protocol, noting the lack of progress in removing the Irish Sea border and recognising that unionist consent for the protocol is not forthcoming, what urgent steps does the prime minister and his government intend to take to honour his commitment to restore Northern Ireland's place fully within the UK internal market and to safeguard the political institutions in Northern Ireland?"

Mr Johnson noted that he and the DUP leader had discussed the issue "extensively".

"He knows that we share a view that the protocol is not working in the way that it needs to in order to guarantee the Belfast/Good Friday Agreement," said the prime minister.

"I don't believe things need to be that way. I think it could be worked differently. And we want our EU friends and partners to understand that and we will continue to work with them to get them to see things in the way that people on both sides of the Irish Sea see them.

"But, in the meantime, Mr Speaker, we do not remove the possibility of invoking Article 16 to protect trade between Great Britain and Northern Ireland."

Afterwards, Mr Donaldson made clear that the sustainability of the political institutions in Northern Ireland were at stake if the Irish Sea border was not removed.

"If the prime minister fails to act to safeguard the political institutions, then it will fall to my party to take all steps necessary to bring this issue to a head," he said.

Earlier, Northern Ireland Secretary Brandon Lewis told the Commons that the "ideal solution" would be to reach an agreement with the EU, but said the UK remains prepared to suspend parts of the agreement.

On Article 16, he added: "We're very clear we don't rule that out.

"If we have to use Article 16 we will, but we are in negotiations with the European Union and the ideal solution for us would be to come to an agreement with the European Union.

"But it's got to be one that delivers on the needs of the people of Northern Ireland."

Micheál Martin said both sides were 'close to' an agreement on medicines

Meanwhile, the Taoiseach told the Dáil that "real progress" has been made in talks between the EU and UK on access to medicines in Northern Ireland.

Micheál Martin said: "We are close to - I would argue - a position on medicines".

However, Mr Martin cautioned that "the devil is always in the detail, and there is some remaining work to be done on that".

Additional reporting PA