The breakup of the UK is “at stake” if a new deal on post-Brexit trading arrangements in Northern Ireland is not reached, a senior DUP politician warned.

Sammy Wilson MP said his party will continue to refuse to let Stormont sit if EU rules aren’t removed in the region – saying this threatens Northern Ireland’s place in the union.

This has been a key sticking point for Prime Minister Rishi Sunak, who is battling to reach a new settlement with Brussels to fix issues with the controversial Northern Ireland Protocol.

The mechanism was agreed as part of the Brexit deal to avoid a hard border on the island of Ireland – which all parties agreed was necessary to preserve peace.

But because the Republic is in the EU, it means traders in Northern Ireland have to comply with single market rules, creating friction on the flow of goods between the region and the rest of the UK.

Mr Wilson told Sky News the DUP wants Northern Ireland to be “treated in the exactly the same way as the rest of the United Kingdom. In other words, that the laws which apply in Northern Ireland are UK laws, not EU laws”.

He added: “Essentially if a deal is agreed which still keeps us within the EU Single Market, as ministers in the Northern Ireland Assembly we would be required by law to implement that deal.

“And we’re not going to do that because we believe that such an arrangement is designed to take us out of the United Kingdom and indeed would take us out of the United Kingdom, because increasingly we would have to agree EU laws which diverge from UK laws and in doing so would separate our own country from the rest of the United Kingdom.”

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There have been reports that Mr Sunak is eyeing a deal with the EU which does not have the support of the DUP.

But Mr Wilson said his party will continue to block the NI Assembly meeting if that happens.

He said the prime minister has a choice whether to “protect the union or the European Union”.

“It’s unreasonable to ask unionists to participate in an arrangement which is designed for the break-up of the union, and that’s what’s at stake here. And that’s why this is a historic moment for the prime minister,” he said.

Mr Wilson accused the government of going into the negotiations with “an attitude of defeat” conceding too much ground to the EU.

Asked if he thought there would be a deal this week, he said: “No I don’t. He (Mr Sunak) realises that there are barriers and hills to climb. He knows the kind of issues that have to be dealt with. I hope he does go into negotiations with a full understanding of what is required.”

Pressure mounting on Sunak

Downing Street said talks are ongoing to reach an agreement with the EU aimed at breaking the impasse over the protocol.

Veteran Tory Eurosceptic Sir Bernard Jenkin said that any deal which did not lead to a return to powersharing at the Stormont Assembly by the DUP – which walked out in protest at the protocol early last year – would be “completely disastrous”.

It is understood Mr Sunak’s officials held talks with their Brussels counterparts on Sunday on how to give local politicians a greater say in the application of EU law in the region, addressing what unionists call the “democratic deficit”.

While it is thought the EU and UK are close to signing off a deal that would reduce protocol red tape on the movement of goods from Great Britain to Northern Ireland, there is no expectation that Brussels is willing to agree to end the application of EU law in the region.

The EU contends that a fundamental part of the protocol – namely that Northern Ireland traders can sell freely into the European single market – is dependent on the operation of EU rules in the region.

Pressure on Mr Sunak is mounting after his predecessor-but-one made a weekend intervention calling for him to take a tougher line with the EU.

A source close to Mr Johnson said his view was that “it would be a great mistake to drop the Northern Ireland Protocol Bill” – which would empower the UK to unilaterally scrap parts of the treaty without the EU’s permission.

A senior government official indicated that a successful outcome of the negotiations would mean the controversial legislation – tabled at Westminster under Mr Johnson’s leadership but paused when Mr Sunak entered No 10 – would no longer be needed.

Mr Johnson’s intervention has raised concerns over a potential rebellion by Eurosceptic Tory backbenchers if Mr Sunak’s changes are put to a vote in parliament.

Some Tories quickly sided with the former prime minister, with Conservative former cabinet minister Simon Clarke and Lord Frost – who negotiated Mr Johnson’s original Brexit deal – urging the government to push ahead with the protocol bill.

Labour will vote with government on protocol

On Monday Sir Keir Starmer repeated that the opposition would back the government to get any deal through.

Speaking to reporters during a visit to Thurrock in Essex, the Labour leader said: “There is a window of opportunity to move forward…the question now is whether the prime minister is strong enough to get it through his own backbenches.

“What I have said on Northern Ireland, the national interest comes first. So we will put party politics to one side. We will vote with the government and so the prime minister doesn’t have to rely on his backbenches.”