Although I know what it’s all about and how it ends, neither Bassett nor Mike Downey and Sam Taylor from production company FAME UK want me to reveal this. The point, they explain patiently, is that the audience will slowly discover the truth about the situation in which the members of Y Company - caught in the murderous trench warfare of the 1915 Western Front - find themselves. Cut off from the rest of their regiment, they stumble across a horror even worse than the trenches.

“What we really wanted to do,” says Taylor, “was to make a film which, in contemporary terms, captured the real feeling of being in the First World War – not something po-faced and stiff-upper-lip and poppies and blood. We wanted something that people would walk out of going, ‘I’d be bloody scared to be in that situation’. We wanted to capture the terror for a contemporary audience.”

It was an ambitious choice for a young company. But FAME seems so far to have escaped the doldrums of the UK production scene, with another co-production, Falcons, already in the bag from last year, and two further productions ready to go this spring. And they have backed Bassett 100% in his determination to direct the script he had spent so long writing. “Other people had said, ‘We can do this for $15 million and give it to an American director. You’ll get paid as a writer and we’ll give you another film afterwards’. My wife goes, ‘That’s a good idea’.

Bell and Speer have a good weather day with the other members of Y Company

“But I say ‘I want to direct it’. And they say ‘No, you can’t. This has got a battlefield in it with 200 people and pyrotechnics, gunfire, action… You’ve got supernatural horror. You’ve got nine principal actors. A first-time film-maker isn’t going to be up to that kind of challenge’.

“Then I met Mike and Sam. They thought about it. I said ‘I’m the only person who understands it. You’ll get some guys who do great TV commercials or great pop promos and it may look better but it won’t mean anything’. They said ‘OK, but you’ve got to do a test shoot’.

Which is what Bassett did, digging some test trenches near his home in Shropshire and filling the sandbags himself (he had to empty them afterwards, as well, because they were only hired). And that is how, a year or so later, he is having fun in the rain and the mud on an airforce base south-east of Prague.

Of course, Bassett likes to tell a good story, in life as much as on the screen, and the truth of the matter is a little less romantic. To start with, everyone was knocked sideways by the screenplay for Deathwatch, which was then called ‘Untitled Trench Thriller Project’. FAME, Downey and Taylor’s recently set-up, German-funded production company, had decided they should do a genre film and sent out a request for horror scripts, which proved to be a process a little like asking a gathering of trainspotters to show you their collection of anoraks.

“Funny things can happen when you’re scared or placed in a frightening situation,” adds Tarver. “We tried to create smart, funny, self-deprecating characters who also provide some humour. Lewis and Fuller, for example, begin to bond as they drive across the country. And there are some hopefully funny things that result from this bonding.”

Where Joy Ride does follow a classic pattern, however, is in not revealing the identity - or even the appearance - of the trio’s nemesis, Rusty Nail. Like the truck-driver in Duel, he is a face never fully seen behind the reflections of the windscreen of his beat-up rig. “He could be anybody, and that makes him scarier,” says Dahl.

writer/director Michael J Bassett protected against the cold and damp in a wet suit (all the actors wore them under their battledress)

“Trucks can be like monsters on the road,” adds Sobieski. “Even in the middle of traffic, it can be intimidating when you’re driving a little car, and all of a sudden a huge truck comes up behind you.”

But this, of course, isn’t in traffic: it’s miles from anywhere in the badlands of Nevada. And, as Zahn laconically observes, it’s on the road where “different rules apply”.

Mostly, says Taylor, the scripts were dire. Then development executive (and associate producer) Sam Lavender read Deathwatch on a train and immediately called Taylor. She then read it on another train (a Eurostar to Paris) and called Downey as soon as it came out of the Channel Tunnel. Downey took it to F&ME’s German parent company, who used the Apollo Media Fund and a German pre-sale to finance the film. Just like that, as Tommy Cooper used to say. “We don’t have to go knocking on a million doors and take two years to get everything done,” says Taylor. “We picked the film up in June, and we were shooting it in October.”

Enthusiasm about the screenplay accounts in large part for the cast, which is a lot more stellar than Bassett - or, for that matter, Downey and Taylor - could have hoped for. It includes Hugo Speer from The Full Monty; Andy Serkis who had just finished playing Gollum in Lord of the Rings; Laurence Fox, son of James, who was recently seen in British genre hit The Hole; and, of course, Bell.

Serkis seems to speak for the cast when he says: “Michael has written one of the best scripts I’ve read in ages. It’s so rare that you see a script that has gone through 10 drafts, and that someone’s taken the trouble to see that through. We don’t generally develop scripts properly in the UK, and this is a rare exception. It’s one of the scariest scripts I’ve ever read.”

“Michael’s ability to choose actors who sit together in an ensemble is amazing,” concludes Downey. “I don’t think there are any other films being made in the UK at present with this kind of level of cast: they are all actors’ actors.”

Bassett, meanwhile, has another reason for being delighted that Bell is in Deathwatch. “The thing is,” he says, “that Jamie probably understands this film better than anyone else.”

“Why?” I ask.

“Because he’s the target audience,” he says.