Broadchurch star Olivia Colman knew the identity of the murderer in the first series of the Tv drama after producers blundered at her audition, and she had to keep the secret all to herself throughout filming of the show.

Colman played a cop hunting the killer of an 11-year-old boy in the British drama's first season, and the true identity of the man responsible was unknown to most of the cast and crew.

However, Colman was harbouring a secret from her co-stars, including David Tennant, throughout filming - she had been mistakenly told the murderer's name at her audition.

She tells U.K. talk show host Graham Norton, "I knew. I asked at my first audition and they told me and then they called me an hour later and said, 'We're not going to do it that way, nobody is going to know, so you're not allowed to know.' So I kept the secret."

Tennant says, "About halfway through series one I was talking to my agent about something and she said, 'So no one knows?' and I said, 'No, absolutely nobody knows', and she said, 'So it's just Olivia that knows?' I was like, 'Olivia doesn't know, we've spent weeks together, we've discussed who it might be and we've taken bets on who the killer is.' She kept that secret brilliantly for months."

Colman adds, "He was so angry when he found out I knew!"