The Northern Ireland Secretary is set to urge unionists to “put the union first” and restore the devolved institutions.

During a speech at the Queen’s University Belfast, Chris Heaton-Harris is also set to warn those intent on violence, they will not drag the region back to its troubled past.

Mr Heaton-Harris will be speaking at a major conference to mark the 25th anniversary of the Belfast/Good Friday Agreement at a time when the Stormont Assembly remains effectively collapsed.

DUP leader Sir Jeffrey Donaldson (Brian Lawless/PA)

The DUP has said it will not participate in the Assembly until its concerns around the Northern Ireland Protocol are addressed.

The party has expressed concerns over the Windsor Framework, which the UK agreed with the EU earlier this year in an attempt to persuade the DUP to call off its Assembly boycott.

In his speech later, Mr Heaton-Harris will say those that want Northern Ireland to remain an integral part of the UK should “put the Union first, restore the devolved institutions and get on with the job of delivering for the people of Northern Ireland”.

He is set to outline the damage being done to Northern Ireland in the absence of a sitting Executive.

He is also set to sound a warning that the continued stalemate at Stormont poses the “single biggest threat to Northern Ireland’s place in the Union”.

The event at the Queen’s University Belfast has seen the participation of major political divs including former US president Bill Clinton, former prime minister Tony Blair and former taoiseach Bertie Ahern.

On Tuesday the Agreement25 Conference will also see participation in a panel event by European Commission vice-president Maros Sefcovic, an address by the Tanaiste Micheal Martin and a panel event with Northern Ireland political leaders, including DUP leader Sir Jeffrey Donaldson and Sinn Fein president Mary Lou McDonald.

Meanwhile Mr Clinton is set to give a speech at the Guildhall in Londonderry.

(left to right) Sir Tony Blair, former US president Bill Clinton and former taoiseach Bertie Ahern on stage during the three-day international conference at Queen’s University Belfast to mark the 25th anniversary of the Belfast/Good Friday Agreement. (Niall Carson/PA)

Prime Minister Rishi Sunak is set to make a closing address to the conference on Wednesday ahead of a dinner event which former prime ministers Boris Johnson and Liz Truss are expected to attend

Addressing day two of the conference, Mr Heaton-Harris will praise the “vision, bravery, leadership and imagination” of the signatories and supporters.

He is set to say the agreement is “crucial” to Northern Ireland’s status today as a “thriving centre of creativity, innovation and entrepreneurship”, and is to reiterate that the Government “remains wholly committed to protecting and upholding” the agreement.

Speaking weeks after the assessed threat from terrorists in Northern Ireland was raised to severe, Mr Heaton-Harris will warn the “small minority who seek to drag Northern Ireland back to its darkest days”.

He will emphasise that they will “never succeed” as the people of Northern Ireland reject “violence which has no place in the society so many have fought so hard to create”.