The restoration of the Stormont Assembly can “fairly easily be done if we want to”, former US president Bill Clinton has said.

Addressing an audience in Londonderry marking the 25th anniversary of the Belfast/Good Friday Agreement, Mr Clinton said an excuse can always be found to say no.

It comes as the Stormont institutions remain effectively collapsed due to a DUP boycott.

Bill Clinton gives a speech to the Guildhall (Liam McBurney/PA)

Crowds gathered outside the Guildhall and an invited audience inside the building rose in a standing ovation as Mr Clinton arrived.

The Making Hope And History Rhyme event, organised by the John and Pat Hume Foundation, also heard musical performances and addresses by young people.

Ash lead singer Tim Wheeler dedicated a performance of his hit Shining Light to journalist Lyra McKee on the fourth anniversary of her murder.

U2 frontman Bono appeared in a video paying tribute to agreement architects John Hume and David Trimble, describing the former as a “man who made all our lives bigger”, and Lord Trimble as the “politician who was seen as a hardliner” but “when the moment came, made the hard choice for peace”.

A video of U2 frontman Bono (Liam McBurney/PA)

Mr Clinton paid tribute to those who came together for the historic 1998 accord, particularly Mr Hume, who led the SDLP and Lord Trimble, who led the UUP.

He described the “gift of the agreement” as “lifting our lives, our children’s lives and our grandchildren’s lives”.

He said it is important to get Stormont back up and running.

“Based on what I’ve heard it can fairly easily be done if we want to, but we can always find an excuse to say no,” he added.

Tim Wheeler of Ash performs the song Shining Light (Liam McBurney/PA)

“If you’re having a fight in your home, you can always find an excuse to say no, if you’re struggling with any kind of relationship or struggle, you can always find an excuse to say no, getting to yes is humanity’s great trial and great goal.

“The people we honour today got to yes.”

Mr Clinton said he can remember virtually every encounter with Mr Hume and Lord Trimble, adding that the latter was “so modest” and never got “the credit he deserved”.

Earlier in the event two school pupils, James Tourish, who attends St Columb’s College, and Ellianna McBride, who attends Foyle College, urged progress.

Ellianna McBride, 18, from Foyle College (Liam McBurney/PA)

Mr Tourish said: “We must stand together united and determined to seek and deliver a better future for all on this island… there is more that unites the people of this province than what divides us.”

Ms McBride said while peace has created the context for politics and for political institutions to work, “those institutions need to function now”.

“The lack of decision-making on pressing issues in healthcare, employment and education is failing our people. We need political stability if Northern Ireland is to become the vibrant, innovative economy and the tolerant liberal society desired by its young people,” she said.