DI Carlisle has it in for Ripley Holden from day one. He takes an instant dislike to the man he's investigating on suspicion of murder… and a shine to the suspect's wife.

David Tennant, who plays the determined detective inspector, refuses to be drawn on his character's principles although he does confess that it's "completely and utterly inappropriate" for him to have an affair with Natalie Holden.

"I won't make moral judgements on the character though, I don't think that's my job, really," laughs the Scotsman, who appeared as the Reverend Gibson in BBC ONE's He Knew He Was Right earlier in the year and has had roles in numerous plays for the Royal Shakespeare Company.

DI Carlisle is drawn in to help out the Blackpool Constabulary when a body is found in Ripley Holden's showpiece arcade. As soon as he meets the hapless entrepreneur, he thinks he's found his man.

But does he believe that Ripley actually committed murder, or is he just out to get him?

"I think it's a bit of both," admits Tennant. "He develops an instant dislike to Ripley, just because of who he is and his arrogance, and he decides that Ripley's the man.

"But that's compounded by the fact that Carlisle ends up compromising himself, so it becomes convenient for Ripley to be guilty too, and it becomes an emotional and sexual thing to nail Ripley.

"I imagine Carlisle is usually very full of integrity and rather good at his job but, for the first time, he finds himself on the slippery slope to madness."

Even his second-in-command, Blythe (Bryan Dick), who has joined him in Blackpool, begins to lose faith in his colleague.

"At first we work very much as a team but as the plot goes on, he sort of becomes my conscience in a way, and tries to muscle me out because he thinks he can solve the case on his own, get the brownie points and move on."

Tennant didn't have to be asked twice to take on the role of Carlisle. He was hooked as soon as he read the first script.

"I loved it. It's so different and so exciting. It's great writing, it's great storytelling, but also with this wonderful device - the songs and the graphic sequences, and the fact that it can move from fantasy to reality and it seems to do so very easily.

"It's brilliant to have a prime-time drama that's so different, and so brave.

"It's really difficult to describe the drama. I think that's good, though, because it means you can't categorise it. It's everything really. It's a family drama, a whodunit, a rite of passage, a love triangle, a musical."

Like most of the cast, Tennant has had little training in singing and dancing: "Not beyond drama school, so the very basic stuff you do there. It's been fun though, dusting down some half-remembered half skills!"

And he says there aren't many jobs around that would find him dancing underneath Blackpool Prom in the dead of night.

"We've found ourselves doing some quite unusual things, like being in a pool fully clothed, or dancing the tango with David Morrissey in These Boots Are Made For Walking.

"And we found ourselves at 3.00am in the concrete colonnades underneath Blackpool Prom, dancing to The Smiths!

"It's been eye-opening and invigorating to get to do all of these things at once."

Tennant says The Smiths track, The Boy With The Thorn In His Side, was the most fun for him to do: "That was the biggest number for me. I had to learn the most dance steps for that one. It's a full-on number with 25 dancers and the actors. It's quite scary!

"Because you're playing the character you tend to be at the forefront of the scenes, but you're surrounded by these dancers who can all do it, and you've got to sing at the same time and act as well… and keep up the psychological thing with the characters, so it's been interesting!

"I also love the Elvis Costello track that's in it, Brilliant Mistake, and there's a great song by The Faces called Ooh La La, which I didn't know, but it's lovely."

One regret he does have though, is not being able to persuade writer Peter Bowker to include a track from one of his favourite bands:

"I was desperate to get some Proclaimers in," he laughs. "I'm a big Proclaimers fan and have been for ever. It would have fitted my accent as well - everything else you have to sing with an American accent, so it would've been nice!"

Tennant is an accomplished theatre actor who has appeared in plays including The Pillowman with the Royal National Theatre, Lobby Hero with the Donmar Warehouse (for which he received a Laurence Olivier Theatre Award nomination for Best Actor), and Romeo & Juliet, The Rivals and The Comedy Of Errors with the Royal Shakespeare Company.

Tennant plays Barty Crouch Junior in the forthcoming Harry Potter And The Goblet Of Fire, which is due to be released next year, and has just begun filming Russell T Davies's Casanova, in which he stars in the title role alongside Peter O'Toole, which is due for transmission on BBC THREE in 2005.

It was while working with the National Theatre in 1995 that Tennant had his first taste of Blackpool.

"It was in the height of summer. I love rollercoasters and we all visited the Pleasure Beach as a company and it divided into who would go on the rollercoasters and who would hold the coats!" he laughs.

"We had a great time up there filming Blackpool. Really lovely people and they were very friendly and helpful," he concludes.

Source: BBC Press Office - 2004