The Lagan Valley MP said he would be speaking with Boris Johnson to warn that stability at Stormont cannot be expected while the Northern Ireland Protocol remains.

He was the only candidate to replace Edwin Poots who announced his resignation following an internal party revolt over his decision to go ahead with the nomination of Paul Givan as Stormont First Minister after a deal was struck between Sinn Fein and the UK Government over the progression of Irish language legislation.

Sir Jeffrey is Northern Ireland’s longest serving MP and was narrowly defeated in the previous party leadership contest won by Mr Poots last month.

He will become the party’s third leader in a matter of weeks, after Arlene Foster was ousted last month and replaced by Mr Poots.

In a statement, Sir Jeffrey said: “The Northern Ireland Assembly is the place where every element of our society is represented. The coalition government is unwieldy, but it ensures every voice is heard.

“Such partnership is how we should move forward. It must be based on respect for each other’s mandate.

“To that end, I will be speaking with the Prime Minister at the earliest opportunity to emphasise that it is not realistic to expect stability when every unionist representative in the devolved institutions opposes the Northern Ireland Protocol.

“The Government and those who claim to be protectors of peace and stability, must step up and deal with the Protocol in a manner which respects the constitutional and economic integrity of the United Kingdom.

“I want to bring stability and encourage everyone to focus on what unites us as a people rather than on what divides us. There has been too much focus on division and recrimination both within unionism and within Northern Ireland.

“I will play my part but the Government and Brussels must step up and recognise the flaws of the Protocol and how it was foisted upon Northern Ireland.”

Announcing the new leader, DUP chairman Lord Morrow said: “The last number of weeks has been difficult for the party and mistakes have been made. Now is the time to move forward in a spirit of humility and mindful that our focus must be on serving the people whom we represent.

“I look forward to the challenges of rebuilding and reconnecting in the time ahead.”

Secretary of State Brandon Lewis tweeted: “I look forward to continuing to work with him and the whole Northern Ireland Executive, ensuring we deliver on the shared interests of all the people of Northern Ireland.”

The Lagan Valley MP said he would be speaking with Boris Johnson to warn that stability at Stormont cannot be expected while the Northern Ireland Protocol remains.

He was the only candidate to replace Edwin Poots, who announced his resignation following an internal party revolt over his decision to go ahead with the nomination of Paul Givan as Stormont First Minister after a deal was struck between Sinn Fein and the UK Government over the progression of Irish language legislation.