Prime Minister Rishi Sunak has hailed his deal on post-Brexit trade arrangements for Northern Ireland as a “crucial breakthrough”.

Several Conservative MPs, including those who supported Brexit, have expressed support for the agreement.

The DUP, whose support will be key to restoring power-sharing in Northern Ireland, said there had been “significant progress”.

But the party warned that “major issues of concern” remain.

And the leader of the Democratic Unionist Party, Sir Geoffrey Donaldson, said that his party will now study the legal text, before reaching a decision on supporting the deal.

The party boycotted the devolved government until its concerns about the Northern Ireland Protocol were resolved, and some Conservative MPs said they would only support a deal if it had the backing of the DUP.

Sinn Féin, the largest party in the Northern Ireland assembly, welcomed the deal, although it said it still needed to examine the details.

The party’s vice president, Michelle O’Neill, reiterated her call for the DUP to return to devolved government, adding: “We have always said that with pragmatism, solutions can be found.”

After months of negotiations and speculation surrounding a potential deal, it was finally revealed during a day of carefully choreographed events.

Talk started from within the government at around 14:00 GMT that an agreement had been reached on an issue that has finally troubled four prime ministers.

The prime minister confirmed the breach shortly after during a joint press conference in Windsor with European Commission President Ursula von der Leyen.

There was a noticeable warmth between the prime minister and Ms von der Leyen when they outlined their agreement on Monday, with the EU chief referring to the prime minister as “Dear Rishi” and hailing a “new chapter” of a “stronger relationship between the EU and the UK”.

With Mr Sunak back in London to address the House of Commons, details of the long-awaited deal have been fine with some MPs who might have been expected to cause political trouble for the prime minister.

Northern Ireland Office Minister and Brexit Party leader Steve Baker said Sunak had “pulled a blinder”.

He revealed that he was considering resigning “late yesterday”, but added that the agreement “should be good enough for any reasonable unionist”.

During a debate in the House of Commons, former Prime Minister Theresa May urged MPs to support the deal – but two other former prime ministers, Boris Johnson and Liz Truss, did not turn up.

No. 10 will be pleased with the US’s response, as outstanding issues over arrangements in Northern Ireland are seen as a hurdle in any potential trade talks between London and Washington.

US President Joe Biden said the deal was an “essential step in ensuring the preservation of the hard-won peace and progress of the Belfast/Good Friday Agreement”.

The agreement, called the Windsor Framework, changes the Northern Ireland protocol, which Mr Johnson signed and entered into force in 2021.

The protocol aims to ensure the free movement of goods across the Irish land border by running checks between Northern Ireland and Great Britain instead.

But under the treaty, Northern Ireland had to continue to follow some EU rules.

Mr Sunak said the new agreement “provides seamless trade across the UK, protects Northern Ireland’s place in our Union and safeguards sovereignty for the people of Northern Ireland”.

But there is no guarantee that it will result in the return of a devolved power-sharing government for Northern Ireland. “Significant progress has been made in a number of areas,” the Federal Democratic Union said in a statement, but concerns remain.

“There can be no hiding the fact that in some sectors of our economy EU law still applies in Northern Ireland,” she said.

The party said it now wants to study the details of the deal and support the legal texts, and will seek “further clarification, re-work or change as appropriate.”

The Social Democrats, Nationalist Action Party and the Alliance Party, which is neither nationalist nor unionist, welcomed the deal, although both said they had concerns about the Stormont brake clause.

But the traditional unitary vote party said the agreement is “a lot of spin, not much substance” and means the protocol “remains effective”.

The Ulster Unionist Party said it would study the details but would not give cover to other parties.

Many pro-Brexit MPs have responded positively to the agreement.

Former Brexit Secretary David Davis said the prime minister had been “tremendously successful in the negotiations” and had “got the best possible deal”.

Former Business Secretary Andrea Leadsom said there had been “tremendous progress,” adding: “It all depends now on whether communities in NI feel it’s the right solution.”

However, other Tory MPs were more cautious, with Sir Bill Cash, the prominent Eurosceptic, saying “the devil is in the details more than ever”.

DUB MP Ian Paisley said the deal “failed” in a number of key areas, including the European Court of Justice’s continued role as the final arbiter in disputes over EU rules.

“My instinct is that he doesn’t cut the mustard,” he told BBC Newsnight.

Sunak said parliament would vote on the agreement at the “appropriate time” but MPs needed a chance to consider the details.

The Labor Party said it would support the deal, but the government would refrain from relying on opposition votes.

Leader Sir Keir Starmer said the deal was not “perfect” but “now that it’s agreed we all have an obligation to make it work”.

Mr Sunak also confirmed that the government had dropped the controversial Northern Ireland Protocol bill, which was introduced under Johnson when he was prime minister and would have given the UK the power to unilaterally overturn parts of the old deal.

He said the bill was now no longer needed and its original legal justification had “fallen”.