Sectarian politics in Northern Ireland were so extreme that when travelling overseas it was customary for politicians from opposing factions to accompany each other to ensure their mutual safety.

That statement was made to Belfast-born Nick Hamm, who grew up during the Troubles. It may have been an apocryphal observation by a journalist, but Hamm took it literally when he discovered Sinn Féin leader Martin McGuinness flew back to Belfast with the Reverend Ian Paisley for the Free Presbyterian preacher’s 50th wedding anniversary during the 2006 peace talks in St Andrews, Scotland.

“These two men had never spoken and they both led from the front,” Hamm says of the reason he has made a film about the event, The Journey (Madman).

“Both exposed themselves to a level of antipathy that most politicians could not deal with. Both embodied the divisiveness and extremism of Ireland. Yet they ended up on a private jet together with nowhere to hide.”

No one knows what exactly took place during a two-hour road trip to Edinburgh Airport, but screenwriter Colin Bateman doesn’t disappoint with his version of what could have happened.

What is known is that the people of Northern Ireland have lived in remarkable peace since these two enemies were able to realise the power of compromise and out of conflict forge the unlikeliest of friendships.

Paisley and McGuinness ruled Northern Ireland as First and Deputy Minister until Paisley, later Baron Bannside, stepped down in mid 2008. He died in 2014. McGuinness died earlier this year soon after resigning from the power-sharing government.

Bringing the story up to date: that government hasn’t been replaced after an indecisive election in January and a lack of agreement between the nationalists and unionists.

Meanwhile, Paisley’s Democratic Unionist Party has boosted its membership in the House of Commons and entered into a confidence and supply agreement with Theresa May’s Conservatives to give her new British government a majority.

The timing for such a film couldn’t be better, as it gives the wider public a better understanding of Northern Ireland affairs.

Timothy Spall (Mister Turner) as Paisley and Colm Meaney (Alan Partridge: Alpha Papa) as McGuinness are perfect in their parts, with the latter initiating most of the attempts at conversation.

Paisley is the much more polarising character, with his firebrand public persona occasionally slipping to reveal a less obnoxious side.

He resists the affable McGuinness until outside events intervene. A walk in the forest and a visit to a disused church add to the suspense as time runs out to meet the airport deadline and a political deal looks highly unlikely.

The car trip is being monitored back at St Andrews, where the British and Irish Prime Ministers are anxious for a breakthrough.

In a generally well cast film, John Hurt is the manipulative political fixer and Mark Lambert is Bertie Ahern in a minor role. Not so convincing is Toby Stephens, who turns Tony Blair into a prat.

Rating: Mature audiences,94 minutes