Chris Chibnall on his Broadchurch follow-up, The Great Train Robbery

He wrote the hugely successful ITV detective drama Broadchurch starring Olivia Colman and David Tennant. Also Torchwood and episodes of Doctor Who. As we wait for the second series of Broadchurch and the US remake renamed Gracepoint, what is screenwriter Chris Chibnall doing next?

His new BBC1 mini-serial The Great Train Robbery, starring Jim Broadbent as Detective Tommy Butler, which is out next month, tells the story of the celebrated heist in 1963 from both the robbers' and the police's perspectives, in two 90-minute films.

"The challenge was to make sure that the drama was weighted so the audience get to see both sides of the story," Chibnall tells me. "That was my reason for doing the piece in the first place. I pitched the idea of seeing the robbery, and the police investigation, from two very different angles, and exploring the resonances, similarities and differences."

A Robber's Tale is directed by Julian Jarrold (The Girl, Appropriate Adult) and stars the up-and-coming Hollywood actor Luke Evans, playing gang leader Bruce Reynolds. Evans who is about to star in the new Hobbit movie, is an actor whom Chibnall feels "lucky to nab before he is off in the stratosphere".

"This is Luke's first ever piece for television and he's hugely in demand in Hollywood right now. But it shows how confident television drama is right now: we're doing things on television now that cinema used to do. It's very exciting," says Chibnall.

While A Copper's Tale about the policemen who went after them, is directed by Broadchurch director James Strong, who also directed episodes of Doctor Who, Torchwood and United, Chibnall's 2011 film about Manchester United's Busby Babes, starring Tennant.

Chibnall whose show Broadchurch was ITV's hottest new drama since Downton Abbey earlier this year, is stepping on more familiar territory with this well-known story that usually focuses on escapee Ronnie Biggs. But Chibnall is paying attention to the planning and execution of the robbery itself. He is also thrilled there is "an absolutely untold story" of the flying squad and Tommy Butler, which no drama has yet touched on.

Did he talk to any of the real-life police in his research? "Yes I spoke to Steve Moore, who is the one surviving member of the train investigation squad – played by Tom Chambers in the film," says Chibnall. "So we had a long conversation and he gave us lots of insight into the investigation and also Tommy Butler."

So how did he come to write The Great Train Robbery? After Chibnall finished the final mix of United for BBC2 in a Soho dubbing studio he was talking to the film's executive producer Simon Heath and director Strong about "other big moments in post war British history". "We felt like it was a really important moment. People knew the headline but not really the detail of what went on," he says.

After they teamed up again, it still took Chibnall two years to write The Great Train Robbery. "The research was the longest part: there are so many accounts, a lot of them contradictory. It probably took me a year to read everything, and to reconcile all the different accounts," he says. "On the police side, it was starting from scratch. There was no single official account of the police investigation. Tommy Butler never spoke to the press, never gave interviews, was never filmed. I was very lucky that historian Andrew Cook had recently managed to gain access to previously locked case files, and he was a huge help."

Now Chibnall is currently writing the second series of Broadchurch. " It will be very different. The only pressure I feel is to tell the story I want to tell as well as it can be told. It'll be a different journey to the first series," he says.

He works from an office near his house in Dorset. "I clock in at 9am, and stay working till 6 or 7pm. You have to put the hours in. Often, I'll work beyond that, if I'm on a roll, or if I'm behind where I feel I should be." He has also written a play for Salisbury Playhouse, called 'Worst Wedding Ever', which opens there in March next year. "It's the first play I've written in 10 years and I'm very excited and utterly terrified about it," he says. "I wanted to make sure I did something very different and challenging between writing Broadchurch series 1 and 2."

Putting Evans who has appeared in Fast and Furious 6, Clash of the Titans and The Three Musketeers on the big screen and Le Week-End star Broadbent together in a scene, he claims, is "every writer's dream". He adds: "But they're also very different performers: watching the two films together is a masterclass in screen performance. I'm in awe of them both and feel so lucky to have written for them."

'The Great Train Robbery' is broadcast on BBC1 next month