Given their track record, you might think that Dick Clement and Ian La Frenais would be spared the struggles that lesser screenwriters go through to see their writing on screen. But this, it turns out, would be naive. Clement and La Frenais may have written some of the best-loved programmes in British television history: Auf Wiedersehen, Pet; Porridge; The Likely Lads; Whatever Happened to the Likely Lads? Their CV may contain the huge hit film The Commitments — as well as more recently acclaimed TV dramas like The Rotters’ Club and Archangel. Yet, when I meet Clement on a solo visit to London, the two most striking things about him are how driven he remains at 81, and how driven he apparently needs to be.

‘What Ian and I both have,’ he tells me, ‘is a sense of being hungry, of wanting to get stuff made. An awful lot of time you spend writing stuff that doesn’t, like architects’ plans that never get turned into buildings. And there’s no job satisfaction in that.’

For this reason, he and La Frenais maintain an impressive policy of always having at least seven projects on the go: ‘You really can’t have any fewer than that. Things will sit there for nine months before anybody does anything. So what are you going to do? Play golf?’ (and with those last two words Clement abandons his normal urbanity in favour of incredulous scorn). At the moment, the list includes Jukebox Hero — a musical built, somewhat improbably, around the songs of Foreigner, which opens in Toronto next month; a musical about Alice Cooper; a play about Harpo Marx; and three TV series.

In the meantime, there’s also Chasing Bono — playing in what Clement acknowledges is ‘a tiny little theatre’. (‘But at least it’s there,’ he characteristically adds, ‘as opposed to being on paper.’) This richly entertaining 90-minute play is a theatrical version of Clement and La Frenais’ 2011 film Killing Bono — a title Clement never liked — which was itself based on the music critic Neil McCormick’s memoir I Was Bono’s Doppelgänger, about how his own dreams of rock stardom fell apart just as his old Dublin schoolfriend was conquering the world. The result shows that Clement and La Frenais have lost none of their stirring ability to combine comedy with an undertow of melancholy. (Think of Whatever Happened to the Likely Lads? where Bob tries to become middle class and ends up miserable — in contrast to Terry, who stays true to his working-class roots and ends up miserable.)

So has any screenwriting partnership ever lasted longer than theirs? I certainly can’t think of one — and neither can Clement. ‘More than 50 years, it’s extraordinary,’ he says in a slightly wondering tone. The two met in the early 1960s in the pubs of Earl’s Court, when Clement was already working for the BBC. The first thing they wrote was a sketch they performed themselves in the classic setting of the upper room of a King’s Road pub — and that featured two blokes called Bob and Terry comparing notes on the dates they’d just had.

‘We realised that we clicked,’ remembers Clement understatedly — and soon La Frenais was showing up at his house every morning at 9.30 so they could write together. And he’s been showing up at 9.30 ever since, these days in Los Angeles where the two moved in the mid-1970s. The move was partly because ‘We thought LA was the head office of the entertainment business’, and partly so that they could translate Porridge (‘our happiest writing experience’) into an American series called On the Rocks (‘one of the most painful. The problem was we didn’t have a Ronnie Barker, so we had to make it into a gang show. The main actor couldn’t carry it.’)

By then, Clement was also a director, whose films included To Catch a Spy, a thriller that he and La Frenais had intended to be light-hearted, until he met his leading man, Kirk Douglas: ‘The first thing he said to me, before “Hello”, was “I can’t play comedy”.’ On the plus side, the film also starred Trevor Howard, who ‘was lovely. He did drink a lot, so in the evenings he was a little sozzled — but he was a delightful man.’

Clement’s directing career meant that he and La Frenais, while ‘still intertwined’, worked separately for a bit. La Frenais created Lovejoy and wrote Spender with Jimmy Nail. Clement did an unproduced screenplay with somebody else, who admitted to feeling like ‘the other woman’ whenever La Frenais popped in.

Before long, though, those 9.30 visits resumed — as did their unusually harmonious relationship. ‘I can remember a couple of minor spats,’ says Clement. ‘But when we do have a falling out, it’s usually because there’s something wrong with the piece. I used to say glibly that Ian was better at dialogue and I was better at structure, but I’m not sure that’s really true now.’ Nor does he agree with the theory that every writing partnership needs a boss. ‘I don’t think there’s a boss with us, and I don’t think there was with Galton and Simpson who were our gods when we started out.’

But that mention of starting out soon returns Clement to his central theme. In the 1960s he and La Frenais wrote two films for Michael Winner. ‘And we thought this is just what happens. You write a script, it gets made and you move on to the next one.’ Now, the scrutiny is much more ‘neurotic’, not just beforehand, but also once the production is under way, with executives supplying screeds of contradictory notes — or, as Clement prefers to put it, ‘talking the whole thing to death’. ‘When we first did The Likely Lads, I was very hurt that nobody from the BBC came to see it. In hindsight we were so bloody lucky that nobody was interfering.’

In the circumstances, Clement and La Frenais, who’s 83 this month, could be forgiven for taking their choice of any number of laurels to rest on. But, luckily for both, neither is keen on doing what Alan Simpson did in 1978, after a mere 30 years writing with Ray Galton. ‘I hate the idea of retirement,’ says Clement. ‘Even when I was 17 I thought “retire” was a miserable word. It’s one thing if you’ve hated your job. But you retire and the next step is the grave.’ And with that, he’s back to his plans for the future, starting with Chasing Bono transferring to a bigger theatre.