James Murray talks about ITV1's new Saturday night series Primeval as being very new, very ambitious and with a script he couldn't put down. But the truth about why he wanted to play monster-hunter Stephen Hart was more basic.

"It's not often in England you get offered an opportunity to be in something so boldly boys' own," he says. "The chance to run around with guns and be chased by dinosaurs doesn't come through the door every day."

So from the costume drama of Under The Greenwood Tree and the soapy intrigue of Cutting It, the actor turns square-jawed action man as part of a team of scientists slipping back and forth in time to prehistoric days in search of long-lost species.

Douglas Henshall is the team leader and brains behind the operation, with Hart as his second-in-command and a man for whom actions speak louder than words.

"With someone like Stephen you know he's the silentish type. I am loathe to say strong, silent type," says Murray of a character whom he describes as a cross between David Attenborough and Ray Mears.

"I knew from day one he was the more hands on, physical member of the gang as opposed to the expositional, explanatory character. I was perfectly happy with that," he says.

He accepted this was fantasy not Shakespeare or Chekhov. As you can tell, he's an actor who takes his work seriously, even hokum like Primeval. To prepare himself for the physical demands of being chased by prehistoric animals he took himself off to Belize for a couple of weeks trekking before filming began.

"I knew the scripts wouldn't demand too much introspective acting. It's not that kind of show," he says. "I did some walking in the jungle. You rough it for three days, then sit in a log cabin to recuperate and then go back out again. That was good fun, but I haven't been wrestling tigers."

There was a lack of creature comforts in Belize but no lack of creatures on screen where he's chased by the fearsome likes of the gorgonopsid and scutersaurus.

Murray got to do most of the stunt work himself. "There are no Tom Cruise type stunts going on, I'm not hurling myself from burning buildings on to helicopters attached to the back of high speed trains or anything," he says.

"It was predominantly a lot of running through woods or corridors either towards or away from some kind of creature. We all became expert at tumbling around and falling over.

"And while I realise that doesn't sound too bad, if you're doing it 20 times over before the director has decided they've got the right shot, it tends to get a bit wearing. That's when you're in danger of hurting yourself. We had a great stunt co-ordinator on set to guide us through the really physical stuff though."

ITV is keen to promote the show as Saturday family evening viewing in the mould of Doctor Who and other fantasy series. Murray isn't very familiar with such shows. "I've not seen them, but that doesn't mean I don't like them. It means I've never really tuned into them," he says.

"I'm very dull with my viewing, I'm more a documentary guy. But I do know what those shows Primeval is being compared to are about. While comparisons are odious, all the things that have been mentioned are great. What they have in common is high suspense and high stakes."

What he found difficult was acting opposite invisible co-stars, pretending he was confronting creatures that wouldn't appear until the Walking With Dinosaurs special effects team added the computer-generated monsters later.

"That was particularly challenging to me and all the cast, that acting to nothing," he admits. "Sometimes there was a ball and stick there, used by the CGI guys to measure height and give us an eye level. Apart from that, it was completely to your own imagination.

"Because it was new territory for everybody, there was a lot of 'we don't quite believe you've witnessed life-threatening dinosaurs' by take three. It's easy to overact and underact."

The actors had an idea of what they were facing through sketches of the creatures and detailed briefings from the people who were creating them in the computer.

All the creature-hunting leaves little chance for romance, although there are signs that something might develop between Hart and zoologist Abby (played by former S Club 7 singer Hannah Spearritt).

Murray hints they won't have time for that sort of the thing - in the first series at least. "There are more important things at stake than whether we can get each other into bed or not," he says.

Primeval begins on ITV1 on February 10.

6:01am Saturday 3rd February 2007