Is there life after Del Boy?

John Sullivan, creator of Only Fools and Horses, has changed tack with a new comic drama about Second World War fighter pilots.

Del Boy Trotter is big in Croatia. The latest magazine from the Only Fools And Horses Appreciation Society, based, naturally enough, in Essex, publishes a letter from a Goran in the ravaged Balkan state begging to see more of Peckham's finest.

John Sullivan takes a puff on his cigarette and tries to account for the worldwide success of his creations, Del Boy and Rodney. Why do two archetypal Sarf London duckers and divers have such universal resonance? Wouldn't most countries be baffled by the Peckham patois? Would they understand phrases like "luvvly-jubbly"? "Wherever you are, you can recognise they're two idiots, Laurel and Hardy almost," Sullivan muses. "Those kind of people are always popular. You know they're going to screw up soon. There's something fascinating about waiting for them to screw up again."

Though we haven't been privy to goings-on at Nelson Mandela House for a year or two, Sullivan, a greying fortysomething in a leather jacket, is still keen to chart the further escapades of the Trotters. Getting the team to synchronise diaries, however, has become the sort of scrape even Del Boy would be pushed to get out of. "Someone is always signed up to something. If Trigger, say, was unavailable, I'd find it impossible to do. Last year David [Jason, who plays Del Boy] was tied up with A Touch of Frost. Then when he was available this year, Nick [Lyndhurst, who plays Rodney] was tied up with Goodnight Sweetheart."

So for the foreseeable future, Sullivan has to face up to Life After Del Boy. He is approaching it with a gung-ho attitude, having just penned and executive-produced Over Here, a lavish, pounds 1.75m, three-hour comedy drama about British and American fighter pilots in World War II. Inevitably, the voice of Del Boy rings through certain lines. A laddish pilot is telling his mates about the tattoo his father had on his private parts in honour of his mother. It read "Gwendoline - well, it was Gwen in the winter".

The film also flies in with enough pure slapstick moments to fill a silent movie. In one incident, an uptight American colonel who is standing in the front-seat of his open-top jeep a la General Patton, orders his driver to halt and, in the oldest trick in the comic-book, is catapulted head first over the windscreen.

But the script manages to sprinkle melancholy into the mirth; the emphasis is just as much on the drama as the comedy. Martin Clunes, who plays Group Captain Barker, a stiff-upper-lip officer with a pipe, a comic moustache and a twitch whenever the Luftwaffe is mentioned, contends that Sullivan's writing always has a sad side to it. "If you look at Only Fools and Horses, there's a melancholy there which we seem to need to make our comedy successful."

But, the writer argues, Over Here is still "a great departure for me. It's very different from what I've done before. You need the sadness to make them rounded characters. You'd be belittling those who took part in the War if you didn't show there was pain and death."

Jacinta Peel, the producer, warns fans of Only Fools' tomfoolery to be prepared for something "much sadder and more emotional. The public have their perceptions of their favourite writers and feel cheated if they get something different. In this, John hits you with a sad note when you're least expecting it."

The film contains some spectacular dogfight sequences featuring Spitfires, Flying Fortresses and Messerschmidts - a far cry from Del coaxing his Reliant Robin round the streets of Peckham. Peel recalls that filming inside the planes "brought home to you just what it must have been like for them - horrendous." To research Over Here, Sullivan read more than 50 books on the War and talked to some of The Few.

Sullivan has contrived to translate his research into a squadron of believable characters - a hallmark of his writing since he first made his name with the jokey street revolutionary, Citizen Smith, in 1977. Sullivan keeps a hoard of them in a file marked "for future use" on his word-processor. He got the idea for Just Good Friends - the "will they, won't they" love- affair sitcom - from a letter in an agony column, and then went through his list finding the right characters to fit the bill. "My characters are from life," he explains, "but you mould them differently. You just alter the clay." He is still trying to find a home for a woman he observed in the audience at The Two Ronnies (for which he used to write) looking at her husband for permission to laugh.

Geraldine James, who plays the haughty mother of one of the squadron, reckons that: "with John's writing, you're not laughing at the characters, you're laughing with them. It's not comedy in inverted commas, it's real life. Take the twitch that Martin's character has. It could be slapstick, but it isn't because something has happened to him which makes him do it."

Clunes concurs. "In John's writing, the lines are not just funny for their own sake; they are funny because they come out of a certain person at a certain time. He's a great listener. Only Fools came from him listening to people in pubs. His scripts are quite hard to learn, but once you make the effort not to paraphrase, it's all there in the rhythms. The beauty of John's writing is that it's non-judgemental. I get sick of seeing films where writers are making a judgement. If someone comes in doing a funny walk, then they've already told you what to think."

Just to prove how convincing Clunes thought his character was, he concludes with a smile: "I did find it difficult to talk to the non-commissioned actors."

`Over Here' is on Sunday 7 & Monday 8 Apr, BBC1