Rishi Sunak has hinted the UK government will press ahead with his new Brexit deal for Northern Ireland even if it is rejected by the Democratic Unionist party, saying the agreement was not about “any one political party”.

The British prime minister arrived in Belfast on Tuesday to sell this week’s agreement with the EU to business leaders, arguing it would unlock fresh investment in the region.

Sunak unveiled the Windsor framework with European Commission president Ursula von der Leyen on Monday, with both sides hailing it as a “new chapter” after years of fraught relations.

On Tuesday morning, the Democratic Unionists, the region’s main pro-UK party, welcomed progress but said concerns remained.

Asked whether the agreement struck with the EU would go ahead without the support of the DUP, Sunak replied: “This is not necessarily about me or any one political party. This is about what is best for the people and communities and businesses of Northern Ireland and this agreement will make a hugely positive difference to them.”

The DUP has boycotted the region’s Stormont assembly since May in protest at the previous agreement with the EU — known as the Northern Ireland protocol — which introduced checks on trade with Great Britain to prevent a hard border on the island of Ireland.

This week’s deal was reached under provisions set out by the protocol for the amendment of its rules, and does not technically require ratification — although Sunak has said the House of Commons will have a vote “at the appropriate time”.

Sir Jeffrey Donaldson, the DUP leader, said on Tuesday that this week’s agreement had made progress “across a number of areas about which we had concerns”. The DUP says the fact the deal went beyond what the EU initially said was possible has vindicated its boycott of the assembly and push for sweeping change to the protocol. But Donaldson added: “We continue to have some concerns.”

The new deal eliminates many checks for goods sent from Great Britain to Northern Ireland, ranging from sausages and medicines to oak trees, allows VAT cuts in the region for products such as beer, and sets out provisions for local legislators to object to new EU rules.

But, despite the calls of some Eurosceptics, it does not end the jurisdiction of the European Court of Justice over Northern Ireland.

Sunak said he understood why unionist politicians would want to take “the time and the space to consider the details” before deciding whether to back the deal.

But he held out the prospect of a big increase in investment should the DUP agree to the deal: “I’ve spent a lot of time engaging with business groups and what they say is if we get this resolved in the way that we have, that will unlock an enormous investment,” he said.

“Remember, Northern Ireland has this very special position where it has access to the UK market, it has access to the EU market which makes it an incredibly attractive place to invest,” he added.

The deal has appeared to mollify even some of the most hardline Eurosceptics in the Conservative party, with early signs that any rebellion from the prime minister’s own backbenches could be limited.

But it was not immediately clear whether it would achieve one of its key objectives: restoring Northern Ireland’s devolved government by ending the DUP’s boycott of the Stormont assembly.

While some Brexiters describe the continued sway of EU law and the ECJ over Northern Ireland as a “democratic deficit”, Sunak said the biggest such deficit was the suspension of the power-sharing agreement in Stormont.

The deal includes one possible incentive to reconvene the assembly. It contains provisions for a new emergency “Stormont brake”, allowing the UK — at the request of 30 members from at least two parties in the assembly — to block updates to EU goods regulations in exceptional circumstances.

“With the Stormont brake . . . the assembly and people of Northern Ireland are in control,” Sunak said.

The prime minister added that the practical steps in his deal would end “any sense of a border in the Irish Sea”. He said there would only be checks on goods moving from Great Britain to Northern Ireland where officials suspect “criminality or smuggling” while Northern Irish businesses producing goods for the UK internal market would only have to follow “less than 3 per cent” of EU single market rules.

The DUP wants businesses and consumers to have “unfettered” access to goods from Britain and set out seven conditions for its endorsement of the new deal, including that there should be no Irish Sea border and the people of Northern Ireland should have a say in the rules that govern them.

Under this week’s deal, a “green lane” with significantly reduced checks would be created at Irish Sea ports for goods destined to stay in Northern Ireland, while a “red lane” would be created for goods continuing into Ireland and the single market.

Donaldson welcomed the so-called Stormont brake but said his party would study the fine print of the deal to decide whether it could “deliver on the areas of concern that we set out in our seven tests”.