The new DUP leader elect has challenged the UK government to “step up and deal” with the Northern Ireland Protocol.
Within an hour of being confirmed as the only candidate in the leadership race, Jeffrey Donaldson said he will speak to Boris Johnson at the “earliest opportunity” around the post-Brexit arrangements.
Earlier, outgoing DUP leader Edwin Poots claimed he had been promised a “significant win” on the Protocol by the UK government.
Mr Donaldson is expected to be ratified as DUP leader following a meeting of party officers on Saturday.
Mr Poots announced his resignation on Thursday 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 Féin and the UK Government over the progression of Irish language legislation.
Mr Donaldson is Northern Ireland’s longest-serving MP and was narrowly defeated by Mr Poots in the previous party leadership contest last month.
He will become the party’s third leader in a matter of weeks, after Arlene Foster was ousted in May and replaced by Mr Poots.
Secretary of State Brandon Lewis was among those who congratulated Mr Donaldson on Twitter.
In his first statement as leader elect, Mr Donaldson emphasised the importance of a power-sharing government at Stormont, describing the coalition Executive as “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,” he said.
“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 Maurice 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.”
Meanwhile Mr Donaldson made good on an early promise – to have the door of the DUP headquarters in east Belfast varnished.
The scuffed-looking door had attracted significant commentary on social media in recent weeks as it became a frequently seen backdrop of turbulence within the party.
The door to the Dundela Avenue premises was painted on Tuesday afternoon.
Mr Donaldson tweeted: “Hope to open many other doors in times ahead for benefit of all in Northern Ireland.”