LINE of Duty creator Jed Mercurio has revealed how Martin Compston only breaks his English accent when he’s "drunk or watching Celtic and shouting at the TV."

British television’s most successful writer, whose credits also include the smash-hit drama Bodyguard, said he had known the Greenock-born actor for three months before he heard his native brogue.

The pair took time out from filming for the latest, eagerly awaited series in Belfast, to host an exclusive Q&A on Friday with 250 lucky scriptwriting students from Glasgow Caledonian University.

Compston, who is soon to be seen in Mary Queen of Scots alongside Margot Robbie and Saoirse Ronan, also told how his co-star Adrian Dunbar ‘fell asleep’ during one of the hit drama’s tense and lengthy interrogation scenes.

The actor, who plays DS Steve Arnot, said the last scene filmed was ‘28-29 pages long’ and revealed his co-star, who plays Superintendent Ted Hastings, wasn’t as gripped as TV viewers.

He said: “There are like mini-one act plays, you earn your money that day.

“When the scripts come out the fear is there, and I’m hoping I’m not in one, but when you’re not in it, you wish you were. The last one we were doing was 28-29 pages, you’re talking 30 minute takes.

“Adrian Dunbar won’t thank me for saying it but he actually fell asleep during one of them!”

Mercurio also recalled his shock at hearing Compston dropping the English accent he uses in the show for the first time, off the set.

He said: “Only two things make him break the accent - drink and Celtic when he’s shouting at the TV.

“The first time I heard Martin speak in his natural accent was when he was drunk. We had probably known each for three or four months at that point.”

Compston, who received an honourary degree from GCU earlier this year, talked about the process of auditioning for the role of DS Arnott.

He said: “My friend Craig Parkinson, who played the Caddy in the show, asked me if I was going up for it and said it was the best thing he had ever read.

“I owe my whole career to Ken Loach, who took a chance on me, and Jed, who put me in front of a wide audience. I never thought I’d be cast as a lead in a primetime BBC show, I just never thought I’d be someone Middle England would respond to.

Professor Ann Marie Di Mambro, who teaches GCU’s MA TV Fiction Writing course. said: “Jed’s visit was an incredible opportunity for our students to get insight and inspiration from one of the best writers in the UK.

“It was also invaluable for them to ask someone of Martin Compston’s standing what actors look for in a script and what they bring to it.”

Filming of the fifth series of Line of Duty started in September and is nearing completion. This is England actor Stephen Graham will star alongside series regulars Compston, Vicky McClure, and Adrian Dunbar as a person of interest in AC-12’s new investigation.