As David Mitchell and Robert Webb say au revoir to Peep Show and hello to a new comedy drama in which they play british diplomats abroad, the pair talk to Sophie Herman about avoiding 'proper jobs'.

David Mitchell and Robert Webb are trying to explain what makes their double act work so well.

'I think we seem more different than we really are,' says Mitchell. 'You can't have people who are really that different working together.'

The myth that the two friends are polar opposites – Mitchell a rule-lover, Webb a rule-breaker – has been bolstered by hit comedy Peep Show, in which Mitchell plays law-loving geek Mark and Webb is drug-taking musician-wannabe Jeremy.

In real life, it's clear the two are very different from those characters. Mitchell is confident and charming, looking dapper in a dark suit and sporting a beard, while Webb, today donning a pink shirt, his ginger hair receding, is relaxed and quieter than his partner. But they clearly have a lot in common.

'Generally I play the one who's got his hands in his pockets, and David plays the one who hasn't got his hands in his pockets,' Webb notes.

The pair have stuck to this rule for their latest show, comedy drama Ambassadors.

At the outset, their characters do not seem a million miles away from their Peep Show counterparts.

Mitchell plays Keith, a British ambassador sent out to Tazbekistan (a fictional ex-Soviet 'stan'), who likes to play by the rules and impress the big bods in London.

Webb is Neil, Keith's deputy, a man who values human rights, speaks the language of Tazbekistan and has integrated with the locals. But over time, the roles become more disparate.

'The key difference with a comedy drama is people are allowed to be competent or even good at their jobs,' says Mitchell, 39. 'Yes, I got to play someone with a brain,' adds Webb, 41.

For sitcom Peep Show, the pair were never required to do any homework. 'We didn't have to research what it was like hanging around in London with no money,' Webb points out.

But for Ambassadors, they spent an evening in the Foreign Office with real ambassadors and, much to history buff Mitchell's delight, did their first read-through of the script in a room where an important 19th century treaty was signed.

The duo discovered a new-found respect for the diplomatic corps. 'They were quietly impressive people who have a terrific sense of humour - we left feeling quite relieved that these were the people we were representing,' says Webb.

But it's a job that neither Mitchell nor Webb feel they could do themselves. 'My parents would have been happier if I'd been aspiring to be an ambassador rather than a comedian,' says Mitchell.

'But I don't think I'd have had the patience to deal constantly with insoluble problems. The great thing about making television and theatre shows is they're short-term issues - you try to tell a story and make people laugh, you either succeed, fail or do somewhere in between, then you walk away. Unfortunately the Middle East situation isn't like that.'

Webb reckons education would have been his calling if he hadn't gone down the comedy route. 'I would have been a deeply underwhelming and not very impressive English teacher for a few years, before stopping and doing something else,' he says. If, by some odd turn of events, they did end up as ambassadors, Webb says he would like to be posted to America, while Mitchell would choose Paris.

'I speak American and we're allies so it should be OK,' says Webb, while Mitchell notes: 'You'd have a nice social life in the British Embassy in Washington. You'd be honorary high society.'

The pair met at Cambridge University during preparation for a pantomime put on by the Footlights, the famous Cambridge comedy troupe, although they can't agree if they met during auditions or after. Whatever, Webb says Mitchell 'made a mental note that I meant business'.

They never really considered stand-up. Having grown up with Blackadder and Monty Python, comedy meant sketches. 'For which you need two people,' Webb points out.

'Exactly, and the smallest amount of people who can do a sketch show is two,' says Mitchell. And so the pair formed a double act.

They started at the Edinburgh Fringe and went on to write for shows such as Big Train and Armstrong And Miller. Their big break came in 2000 when their sketch show Bruiser was shown on the BBC.

By the following year they had a new sketch show, The Mitchell And Webb Situation, on Play UK, which was later turned into a BBC Radio 4 show, That Mitchell And Webb Sound, which was followed by That Mitchell And Webb Look back on television, but this time on the BBC. They also appeared on the big screen in 2007 film Magicians.

In between, in 2003, the pair first appeared in Peep Show, written by Sam Bain and Jesse Armstrong.Unfortunately for fans of the sitcom, it is taking an indefinite break after the upcoming ninth series.

But the good news is that the pair say it's not necessarily the end for Mark and Jez.

Ambassadors starts on BBC Two tomorrow.