Steven Moffat looks back on Coupling and reveals why he turned down a fifth season

The series, which explored the friendships, dating lives and sexual misadventures of six friends in their early thirties, was based at least in part on Moffat's own life and the early stages of his relationship with television producer Sue Vertue (now his wife) – he recalls first pitching it to her, after a fashion, following "a boozy lunch" with a friend. "I turned up at Sue's office, which was at Tiger Aspect at the time, slightly worse for wear, and wrote the word 'Coupling' down on a piece of paper or an envelope or something – and I said to her, 'Remind me to talk about this later'."

She did, and Moffat later laid out his concept for a comedy series about the early stages of dating, when you're "playing at being a couple" but can't quite shake the mindset of being single. "It's role play. You don't really know what you're doing. You really are just saying, 'Look at this, we're so grown up – we turn up places together, we send joint Christmas cards...'

"It just feels like an awful lark, as opposed to what it becomes later. It becomes much better later. But, you know, it's really not the same life as you're leading a few years later when you've got kids and you really are welded together."

Describing himself as a "nervous introvert", Moffat was also keen to explore what he calls "the terror" of dating, with his mixed feelings on the matter being personified in Coupling's lead characters. "I never really even thought of them as a group of friends, I just thought of them as different bits of my brain – particularly the three boys. It's the brutally confident one who wants a shag [Patrick, as played by Ben Miles], the absolutely terrified one who also wants a shag but can't get past his own terror [fan favourite Jeff, played by Richard Coyle] and the negotiation in the middle of those two impulses, which was Steve [played by Jack Davenport]."

Back then, Moffat says he wasn't at all nervous about pulling from his own life and experiences and putting it all on-screen. "I probably would be now, but it was a less censorious time. So no, I was quite gleeful about it. I mean, also, there's nothing like hiding in plain sight. You know, journalists would ask us at the time we were making it, 'Are any of the characters based on you and Sue?' and I said, 'Well, have you looked at the names?' – they would be genuinely astonished, they hadn't noticed that the two main characters have got our names, and indeed live in our house, because the location we used for Steve's flat was actually our house at the time."

Though the characters played by Jack Davenport and Sarah Alexander did indeed take their first names from Moffat and Vertue, he insists that naming the former's character "Steven Taylor" was not in fact a nod to the Doctor Who companion of the same name played by Peter Purves. Instead, it was a nod to Moffat's previous BBC sitcom Joking Apart, which was again semi-autobiographical and featured Robert Bathurst's character Mark Taylor as his surrogate. "I just thought I'd make [Steve] the unknown brother by giving him the same surname and then realised, of course, it was the name in Doctor Who. But you know, in all honesty, nobody knows that. I mean, if you even know that Peter Purves was in Doctor Who, I bet real human beings don't know what his character's name was."

Cast alongside Davenport, Alexander, Ben Miles and Richard Coyle were Kate Isitt as Susan's neurotic best friend Sally and Gina Bellman as Steve's possessive ex-girlfriend Jane. Though aspects of each character were originally based off of Moffat's own neuroses, he says the actors' own personalities quickly began feeding into their on-screen personas: "You start writing their voice quite early on and that ends up completely supplanting what you imagined they sounded like."

Moffat wrote every single episode of Coupling, with a single director also helming all four seasons: Martin Dennis, already a sitcom veteran by the late 1990s having helmed episodes of 'Allo 'Allo, The Upper Hand, and Men Behaving Badly, and still in demand today with recent credits including Friday Night Dinner and The Goes Wrong Show. Dennis was, Moffat says, "adroit, as you'd expect, with jokes – which is why everybody wanted him and still want him".

"Martin has a great precision about how jokes work, and how you keep actors under control over the few days of rehearsal. Rehearsing a comedy is rather grim, because it gets less funny every time you do it. On the first day, it's hilarious, then everyone gets bored of the jokes and starts putting extra bits in... 'Wouldn't it be hilarious if I tripped over the carpet as I came in?' – Martin would keep in his head what was funny about the joke when he first read it, or when he first heard it at the readthrough, and preserve that and not lose confidence."

Rehearsals for Coupling took place in a church hall off Kensington High Street, with episodes then being filmed both on location and at Teddington Studios in Richmond upon Thames (since demolished to be turned into housing). The experience of debuting his scripts in front of a live studio audience was not, Moffat admits, his favourite part of the production process. "Oh, it's awful. I can't tell you how awful it is. I used to simply write the word 'help' on the back of my scripts. I think Sue's still got some of them.

"Sometimes it goes wrong. Sometimes an actor muffs the line before your best joke. Sometimes – in fact, frequently – you have to do the scene several times, so your jokes are trotted out again, in front of a studio audience that have already seen it and are desperate to get to the next part of the story, and if that scene contains a joke that doesn't work, and is dying, that's even worse."

The reaction of the audience on the night was also rarely reflective of how an episode of Coupling might later be received by fans and critics, Moffat suggests. "[Studio audiences] are not a reliable barometer. They're having a very different experience from the people who are watching it at home.

"The best sitcom audience responses I've ever heard – genuinely, and I've been to loads of sitcoms, including all of my own – were from my absolute disaster, Chalk [aired for two seasons on BBC One in the spring and autumn of 1997]. It got riotous responses – we had to cut down the laughs they were so long and so glorious! But on television, everybody absolutely f**king hated it. Hated it beyond reason.

"Indeed, the episode that sort of put Coupling on the map was [season one's] The Girl with Two Breasts, half of which was in Hebrew. It died a death on the night and we felt we had a terrible episode. We even moved it in the running order to episode five so people wouldn't notice it. It was actually our most popular episode."

The bilingual nature of The Girl with Two Breasts was just one of the ways in which Coupling played with the sitcom format across its four seasons – other examples include season 3 opener Split using a split-screen effect to follow both Steve and Susan in the aftermath of their break-up, and season 4's Nine and a Half Minutes depicting one sequence of events from three different perspectives. "It seemed to suit it, because an awful lot of Coupling was different perspectives on the same subject," Moffat says of employing these different techniques. "But the honest answer is, I just love that sort of thing. I will watch any film if there's a negative review that says, 'Oh, this film is all pointless formal trickery and narrative hijinks' – I think, 'Right, I'm watching that, that's for me!', I love that sort of thing."

Coupling earned a warm reception when it premiered on BBC Two in May 2000, with The Times hailing Moffat as "one of the boldest, most inventive, sitcom writers around" and The Guardian likewise praising the show for its "comic writing of astonishing originality and invention". It won the Silver Rose for Best UK Sitcom at the Rose d'Or Light Entertainment Festival in 2001 and triumphed in the Best TV Comedy category at the 2003 British Comedy Awards, while viewing figures were healthy enough to secure several more seasons and spark interest abroad, with short-lived US and Greek remakes following.

Following three hit seasons, however, the show was dealt what Moffat now admits was "a grievous blow" as Richard Coyle opted not to return as Jeff for a fourth run. Addressing his exit in 2008, Coyle said it was "a very difficult decision" but cited fear of typecasting for his sudden departure. "I was very keen that that character didn’t stick with me. It’s the kind of character that does."

The problem, Moffat now suggests, was "not so much that [Coyle] was leaving, but that he didn't do a goodbye episode" despite efforts to convince him to return for a one-off.

"The departure of a beloved character is a gift to a show, not a problem, so long as you can write them out. Then it's an absolute gift to any writer – you think, 'I'm going to write out the most popular character', that is a boon, there's nothing wrong with that, so long as you give them a grand finale that is so good and satisfying you actually don't want them to come back. You know, the way Russell [T Davies] wrote Rose out in [Doctor Who episode] Doomsday all those years ago is so magnificent that it doesn't hurt the show at all. But you need to have the curtain come down.

"So it's a very steep hill to climb, to replace a character without having said goodbye. It doesn't look like a chapter in the story, it looks like a staffing problem, which is exactly what it is."

The fourth season of Coupling, which launched in May 2004 on the then-fledgling BBC Three (followed later by a BBC Two repeat airing), introduced a new character in Jeff's place – sci-fi geek Oliver was played by Richard Mylan, who Moffat says is "an outstandingly good actor" but faced "a tough job" in replacing the show's breakout character.

"Had I known that there was only one more run, I probably wouldn't have attempted to replace Jeff," he admits. "And part of me does wonder if the bolder decision might have been just to carry on with the other five characters and let them get on with it. It's not like all the shows centred on Jeff, though probably the most popular ones did."

Though it was to be the show's final outing, season 4 wasn't always intended as such – in fact, a fifth season was green-lit by the BBC, only for the creative team to ultimately choose to walk away. "It's probably not remembered this way, but series 4 did perfectly well and they commissioned series 5, it was going again," Moffat reveals. "But I remember talking to Sarah Alexander and she was like, 'I'll do it, but... what are we doing? Is there anything else to do?' and I remember thinking, 'I don't think there is, I'm not excited.' So we handed back our green-lit series and said 'No, we think it's done.'"

Looking back, does any part of him regret turning down that fifth season? "It's not a lot of fun if you've lost faith. I loved working on that show, but I was worried that what we were doing in the end was loving working on the show rather than loving the show we were making, which is to say the least a big difference."

Moffat is similarly cool with regards the prospect of a revival featuring the original cast – given how tied the show was to a particular time in the lives of its central characters, he's not even convinced if they'd all still hang out. "It was a show about dating. It was called 'Coupling', not 'Couples', because they weren't really a couple yet. You're just sort of setting up the props and getting ready for the main event... so I don't know if it would ever work again.

"Of course, you could make anything work, but what is the show about now? You know, would they be talking about kids? Maybe it would work? I don't know. Possibly, possibly. No one's asked me."

Coupling stands as Moffat's final TV sitcom to date – having established himself as a writer of comedies, he's more recently found success as showrunner on a string of blockbuster dramas, from Doctor Who and Sherlock to the forthcoming Inside Man for the BBC and The Time Traveler's Wife for HBO. Would he be interested in returning to the genre that originally made his name, or has he left all that behind? "You give me pain," he says with a chuckle. "I've written a couple of comedies, but no-one wants them. I've had two comedy scripts rejected, so maybe my sense of comedy is now hopelessly dated. It possibly is, because I'm kind of farce-driven.

"But I really do like writing comedy, and I'm not absolutely sure I ever stopped, I know I get in trouble every time I say this, but Sherlock is kind of a comedy. It's a comedy about a mad detective. I mean, I think it would be stretching a point to say it's a detective show! The original stories are very funny – that's usually missed when people make versions of it, but they are sort of entertainments...

"And Doctor Who is full of gags. Russell and I certainly wrote it with a heavy emphasis on the fact it's funny – it's the only funny sci-fi show. When you go to a Doctor Who press launch and there's a big audience, you'd think they were watching a comedy – they laugh a lot. And, you know, not just at the special effects! If you don't have a Game of Thrones budget, you can have better gags."

All four seasons of Coupling will arrive on BritBox on Thursday, 20th January – read our guide to the best series on BritBox or find something to watch tonight with our TV Guide.