Line Of Duty actor Martin Compston has revealed his time spent in quarantine was two weeks of “water, soup and an exercise bike” so he could fit back into his character’s suits.

The actor, 36, plays DS Steve Arnott in the popular BBC drama series, created and written by Jed Mercurio, which returns to BBC One on March 21.

The series will feature seven episodes and also sees the return of Vicky McClure as DI Kate Fleming and Adrian Dunbar as Supt Ted Hastings.

DI Kate Fleming (Vicky McClure), DS Steve Arnott (Martin Compston), DC Chloe Bishop (Shalom Brune-Franklin) and Superintendent Ted Hastings (Adrian Dunbar) (World Productions/Aidan Monaghan/Steffan Hill)

New additions to the AC-12 team include Shalom Brune-Franklin and Scottish star Kelly Macdonald, who makes her debut as guest lead Detective Chief Inspector Joanne Davidson.

Compston said: “This series has been a shoot like no other. We shot in the middle of a pandemic and it was interesting when we stopped for the first lockdown. Nobody had any idea what was going on and it was such a surreal feeling.

“Before we stopped, there was the looming threat of being shut down hanging over us. It’s quite hard to get into work in the morning and get yourself motivated when everyone is worried about getting home.”

He added: “The biggest thing for me was when we started, I had just come off the job called The Nest and I had a few topless scenes in the show. I was probably in the best shape of my life. So, when we started the job at the beginning of the year, I was in pretty good nick! Then lockdown happened – we all ate too much, drank too much.

“When I came back to the UK and had to quarantine, I asked our lovely costume designer to leave Steve’s suits in my room so I could try them on as they were all tailored.

“That was a really tough day – I was bursting out of everything! I didn’t realise how the suits were quite so tailored to my original shape!

“I thought quarantine was going to be wine and pizza, but it was water, soup and an exercise bike for two weeks! I was chuffed to get out of it.”

Scottish star Compston lives in Las Vegas with his American wife Tianna Flynn.

Asked about his character in the upcoming series, he said: “At the beginning of the series, Steve is still a DS. So, still no promotion but he is chasing! He has got bored as AC-12 is now tainted and the investigations have been severely curtailed.

“At the start, he is chasing up mundane cases, similar to chasing Lennie James over the expense of a bacon roll in the first series! Steve thrives on the thrill of the chase and the adventure of it so he’s a bit lost and having issues both physically and mentally.

“He definitely sees himself as a bit of a Sherlock Holmes with a waistcoat. Every year with Line Of Duty, these scripts are a gift and we get more into the back stories of each character through Jed’s writing. If we deliver what’s on the page, we are on to a winner”.

Line Of Duty returns to BBC One on Sunday March 21.