British opposition Labour Party Leader Keir Starmer said on Monday that he expects his party to back a new deal on post-Brexit trading arrangements for Northern Ireland.
"This is going to be an improvement on what we've got, which is why I say with confidence we expect to be able to back the deal," Mr Starmer said.
"We've got to make progress, I think we owe it to the people of Northern Ireland to get on and fix it."
European Commission president Ursula von der Leyen and British prime minister will announce a new Brexit deal for Northern Ireland on Monday if the two can agree final details during lunchtime talks in the UK.
The deal seeks to resolve tensions caused by the 2020 post-Brexit arrangements governing the North, but it remains to be seen whether it will go far enough to end political deadlock in Northern Ireland and satisfy British critics.
Ms Von der Leyen will travel to the UK for "late lunchtime" talks, after which Mr Sunak will convene a meeting of his cabinet. His office said if a deal had been reached, it would then be announced at a joint news conference and afterwards to the British parliament by Mr Sunak.
"The prime minister wants to ensure any deal fixes the practical problems on the ground, ensures trade flows freely within the whole of the UK, safeguards Northern Ireland’s place in our Union and returns sovereignty to the people of Northern Ireland," a statement from Mr Sunak's office said.