Sir Jeffrey Donaldson is set to become the DUP’s next leader, as he warned Boris Johnson on Monday that the "failure" to fix the Northern Ireland Protocol could throw the future of power-sharing into doubt.

In what is expected to be an effective "coronation", Sir Jeffrey, the party’s Westminster leader, has confirmed his second leadership bid and is now poised to replace Edwin Poots, who was forced out last week.

If no rival comes forward before 12pm on Tuesday, he will be confirmed as leader by the weekend. He will be the DUP’s second leader since Arlene Foster was forced out at the end of April.

Urging the DUP to set aside weeks of fierce infighting, Sir Jeffrey said the party needed to "unite in the face of the threats posed to Northern Ireland by the protocol".

In a clear warning shot to the Prime Minister, he added that the protocol, set up to prevent a hard Irish border after Brexit, was the "number one issue facing our country, our people and our place within the United Kingdom".

It comes days after senior DUP figures told The Telegraph that the party could effectively threaten to collapse the Stormont Assembly unless Mr Johnson acted swiftly to resolve the significant trade disruption the protocol was causing in Northern Ireland.

In a statement issued on Monday, Sir Jeffrey said: "If elected, I will ensure that the Government doesn’t just listen, but recognises the need to take decisive action to deal quickly with the protocol.

"A failure to act will undoubtedly have consequences for the stability of our political institutions and the prosperity of our economy."

Sources in Belfast said on Monday they expected Sir Jeffrey to vacate his seat in Westminster and stand to become an assembly member at Stormont.

It is unclear whether a DUP assembly member will make way for him immediately, or if he will remain in the UK Parliament until the assembly elections are held.

He is expected to become First Minister if he secures an assembly seat, meaning Paul Givan, who has been in the post for less than a week, would be forced to step down.

Sir Jeffrey could also force early assembly elections unless the UK Government withdraws its commitment to legislate from Westminster on protecting the Irish language if this has not been done in Northern Ireland by 30 September.

It was the price demanded by Sinn Fein for continuing power-sharing, but it has enraged unionists, who have accused ministers of interfering in devolution.