Broadchurch series three was shrouded in so much secrecy that even leading man David Tennant was driven up the walls. 

The production team went to great lengths to keep the twists and turns of the upcoming plot under wraps, issuing special passwords and individually watermarking scripts, and Tennant says “everyone found it rather exhausting”. 

“We were all issued with different passwords for different things,” he reveals in an interview in this week’s Radio Times.

“So new bits of script would come through and you’d forget what your password was and have to phone somebody up and prove it was you,” he explains. “That drove me mad, if I’m honest. I’d phone up the office and go, ‘I need it on paper, I can’t cope!’”

It’s not the first time he’s found himself frustrated with the level of secrecy on set, though. During the filming of the show’s very first series Tennant was left in the dark about the identity of Danny Latimer’s killer while his co-star Olivia Colman was let in on the secret – simply because she asked.

“David was quite cross with me for that,” says Colman. “But once you start pretending, you sort of believe it. Then because all the performances were so good, you begin to think, ‘Oh maybe it’s not them’.” 

“I just thought it was quite funny, even at the time,” he laughs. “But she’s quite tortured by the fact. So I can use it. Even now it remains a weapon to taunt her with.”

Broadchurch series three debuts on ITV on Monday February 28th at 9pm

Read the full interview with David Tennant and Olivia Colman in the new issue of Radio Times magazine, out on Tuesday in the shops and via iTunes