In the ornate surroundings of the Cadogan Hotel in Knightsbridge, Nye, sporting an appealingly unkempt beard, defends the sit of his new com: a drab suburban solicitors' office. "I like basic situations. I've done a basic domestic situation with Men Behaving Badly. Now I'm doing a basic work situation. After all, most people work in offices. I used to; I was a translator for an insurance broker and then for Credit Suisse - I didn't seek much excitement in my early life. I like office life - it's just people sitting around chatting. For a writer not interested in plots, that's good."
This setting also provides the writer with what he enjoys most: gloominess. "Is It Legal? has a staid firm in a pretty run-down locale," he avers. "It gives that slight air of desperation that I like so much. Characters come built-in with this desire to escape. Eventually, the time will come when I have to do successful people, but I'm sure some boffin could come up with the statistic that 83 per cent of sitcoms are about desperate people - and the rest aren't very good."
It is rare for a writer to be touted as the star of the show, but after his previous two works, that is what Nye is. Along with such people as Ben Elton, Richard Curtis and Jennifer Saunders, he is one of the handful of comedy writers whose name appears above the title. At the launch of Is It Legal?, I was in danger of drowning in a sea of tributes.
"Simon develops characters fantastically well," says Patrick Barlow, co-star of the series. "You don't feel you're playing a caricature. He's not frightened of being psychologically accurate. It's nice to get laugh- lines, but it's almost as rewarding to do lines that are actually quite touching." Imelda Staunton, Barlow's co-star, grabs the baton. "He's good at making people vulnerable - think of Frank Stubbs - and he's not afraid of violence and mental cruelty. If you haven't got words, then no amount of face-pulling will cover that up - as I've learnt to my cost. But with this you've got no need to cover anything up."
Luvvieness aside, it is true that Nye's great knack is to be on first- name terms with his characters. They have that quality without which no comedy will work: believability. We've all met people like the loveable loser Frank Stubbs, the incorrigible Men Behaving Badly, Gary and Tony, and now the sadly unfulfilled office workers Stella (Staunton) and Bob (Barlow).
Having become a full-time writer relatively late in life, Nye remains refreshingly modest about his achievements. Of his finest hour, Men Behaving Badly, he says: "It's just self-deluded people chatting to each other endlessly. It isn't any great thesis about the young man in society or sexual politics. It should be said that idle conversations are taking place up and down the country that are far funnier than what we see on television. They're just not being recorded. That's what I was trying to do - take some idle conversations and shape them into this story of rivalry."
The success of Men Behaving Badly has led some people to confuse the writer with the archetypal lads of the title. "I can quite believe it is a side of me that I've suppressed and that I'm now given a great opportunity to express. But nothing appalls me more than some of the things they do. I don't even go into the pub much any more. I've got a baby, for goodness' sake. I like writing it, but I don't like doing it. The show is not championing anyone. People just like to see stupid behaviour. It's liberating. It's seven-and-a-half hours of stupid behaviour."
Surprisingly, those seven-and-a-half hours have copped little flak. "My sister has been the only person to complain," Nye says, half-regretfully. "She introduced me at the christening of her fourth child as 'the rudest man in England'. I thought, 'Have I gone too far here?'. But it's the only way to do it. Once you've chosen your characters, there's nowhere to go but rude. For a lot of people, it obviously stays within the limits they've laid down. I still don't know if I'd want to have any children of mine watching two actors singing the Wanker Song in a pub. I'd do some judicious sending to bed."
Millions of viewers obviously disagree, staying up late to go in for some vicarious bad behaviour. So what's the secret of his success? "William Goldman said you need six brilliant moments in a film to make it worthwhile. The same applies to a sitcom. Half a dozen sparky moments and you're laughing." Nye certainly is - all the way to the bank.
'Is It Legal?' starts Tuesday, 8.30pm ITV