How have David Mitchell and Robert Webb changed since Peep Show began?

How will the actors who have played the pitiably deluded “El Dude Brothers” since 2003 feel on the last day on set?

“Gutted,” says Webb immediately, nostrils flaring with just a suggestion of his “incredibly petulant” character. “It’s a heck of a thing ’cause we’ve done it for 12 years.”

“I think it will be very sad,” says Mitchell with the mournful cast of his “tweedy idiot” on-screen alter ego.

When we first met the pair of ageing graduates from the fictitious Dartmouth University, they lived in an ex-council block in Croydon. Mark was an office drone and Jeremy a wannabe musician, but what united them was their desperate social lives and even more desperate romantic circumstances.

In what will be the 49th episode of Peep Show we find them, still, frankly, losers. They are in a huff with each other after a picnic that was “electric” in all the wrong ways where Jez declared his love for Mark’s girlfriend, Dobby. They haven’t spoken for three months and now there’s a cuckoo in the nest – Mark has a new flatmate, Jerry, played by comedian Tim Key, and a “bitter, envious, furious” Jeremy has vowed to eject him.

So, nine hilarious series on, they have, alas, not gone very far. Yes, there has been some personal maturation (Mark has had a child, albeit not one that lives with him), but also some catastrophic missteps (Jeremy once ate a dog, albeit not willingly… not entirely willingly). Yet the pair remain stuck together, bound by what Webb calls “inertia”. Or, as Mitchell characterises it, “Nothing’s gone right enough for either of them to get away.”

But this, they agree, is the right time to say goodbye, as Mark and Jeremy flail towards the milestone of their 40th birthdays. “Sam and Jesse have been saying, and we’ve been agreeing, it’d be nice to come back to them in a decade or so,” reveals Webb. “But this has definitely got to be the end of Peep Show in its initial incarnation. Because it’s about young men. And we’re now middle-aged, just about. This series addresses…”

“…the ageing process,” interjects Mitchell with the thought-finishing synchronicity that comes with being in a career-long double-act. “But if new people came and just watched this series, it would totally make sense. And then hopefully they’d go back and watch the ones where we look younger.”

“’Cause we were,” sighs Webb, as if he almost can’t believe it himself.

Mitchell, 41, and Webb, 43, have been comedy partners since they met at Cambridge University’s Footlights. Post-graduation they had some success writing and performing “bits and bobs” in TV and radio sketch shows. What kind of double act were they when Peep Show came knocking ten years into their career?

Mitchell and Webb in the first ever episode of Peep Show

“A very relieved double act,” smiles Webb. “But I’d like to think we’ve stayed the same. We were both nudging 30 by the time the show came along, so it’s not like we went mad with fame and power.”

“Also,” continues Mitchell, “if we’d had that break in our early 20s, we’d have probably been a bit more blasé about it – ‘this breaking into comedy thing doesn’t seem that hard.’ But we were aware that it was hard, and that sitcoms can go down as well as up, as they say."

Theirs was a gentle rise over eight series of Peep Show: a solid if unremarkable million viewers every time, bolstered by passionate fans, a healthy afterlife on DVD and a handful of comedy awards, including two Baftas. Accordingly, there were no crashing-the-Lamborghini moments of fame-inspired recklessness. Unless we count Mitchell’s class-A addiction to appearing on panel shows.

“When it was really going great guns, we were too busy to go mental,” notes Webb. “And we were both the kind of people who, even before we left our 20s, wanted to go to the kind of pub where you get to have a sit down.”

“What it meant for us really,” he continues, “was access to mortgages where we could buy slightly larger places to live.”

It is indeed with regard to their circumstances that Mitchell and Webb can divide their lives into pre- and post-Peep Show.

Mitchell (fondly): “Rob hasn’t massively changed. Although he’d admit himself he’s lost a little hair.”

Webb (ruefully): “There’s been some hair under the bridge.”

Mitchell (cat-that-got-the-cream smile): “But what he wasn’t when we started the show, and I wasn’t either, was married or a father.”

Webb (still-hurting grimace): “I was recently dumped when we did the first series. That was the kind of support that she was showing as we did our first Channel 4 sitcom.”

But things turned out for the good. Webb first encountered his wife of eight years, actor/writer Abigail Burdess (above), on Radio 4 sketch show Concrete Cow. They have two daughters aged four and six. “She came on, her friend was in the audience and she told her that every time she came up to the microphone, I was staring at her bottom. That alerted Abi to the idea that I had shown an interest."

Mitchell met his future wife, newspaper columnist and Only Connect presenter Victoria Coren (below), at a film premiere in 2007; their daughter Barbara was born earlier this year. Presumably being a “telly couple” can’t help but ratchet up the fame quotient?

“It increases the slight self-consciousness [in public],” he acknowledges. “If you are ever seen to use the fact of your being part of a couple where you’re both a bit known to get anything, in the long run the press punish you.”

Nonetheless, although the concept seems ill-fitting for these almost pathologically unassuming blokes, some Peep Show-catalysed “celebrity” has crashed into their lives.

Webb recounts how, “We were asked to do the voices of baddie robots in Doctor Who [in 2012, below]. I did mine camp, knowing how much it would annoy David, as he’d have to do the same thing. But one of the unexpected consequences of that is that it doubles the amount of time it takes me to get out of a stage door when I’m doing a [theatre] show – because Doctor Who fans come along with pictures of robots that they want you to sign.”

Webb may have appeared on the stage away from Mitchell in Jeeves and Wooster and Mitchell hasn’t shaken that panel show habit. But in the last decade they’ve also made a film together (Magicians), toured, starred in those annoying Apple Mac ads, written a sketch show (the BBC’s That Mitchell and Webb Look, another Bafta-winner) and starred in other comedy series together (The Ambassadors). Do they ever get on each other’s nerves?

“There have been points where we’ve been working together so intensely that we’re sick of the sight of each other,” concedes Mitchell. “But there’s never been a point where we’ve seriously contemplated stopping working together. We clicked when we met, and very quickly felt that, as a double-act, we were greater than the sum of our parts. So while Peep Show was our big break in terms of people knowing who we are, our greatest break was starting to work together as a team,” he concludes, gazing deeply into his partner’s now-moist eyes.

Before they hurry back to set (and before there’s some serious manhugging that’s frankly embarrassing for all concerned): what ambitions remain? “To keep doing what we’re doing,” replies Mitchell. “We love doing British TV comedy. Neither of us have great ambitions to go to America – although I’m not saying we would turn down a juicy part.”

“We want to be the old farts sitting around on BBC2 and Channel 4,” affirms Webb, “getting in the way of younger comedians.”

Mitchell likes the sound of that. “If in a few decades we can be in the position Barry Cryer’s in now, we’ll be very happy. He’s an inspiring figure in British comedy.”

What about this new C4 sitcom of which we hear rumours, written for them by Simon Blackwell, who has worked on The Thick of It and Veep and collaborated on Peep Show?

“It’s a good idea,” says Webb, enigmatically.

“Very different from Peep Show,” says Mitchell, coquettishly. “It’s very much a comedy about middle-aged men.”

Do they play a pair of dysfunctional detectives with drinking problems?

“No!” exclaims Mitchell, eyes widening, “but now I like Simon’s idea less. That sounds amazing…”

Peep Show returns to Channel 4 today (Wednesday 11th November) at 10pm