Alistair McGowan is grumbling about David Cameron. No surprise there, perhaps – the Prime Minister has his share of detractors. But McGowan’s gripe is a niche one. “His voice!” he says.

“It’s like nobody else’s I’ve ever heard.

He sounds like his whole face is covered in cotton wool and his voice is buried deep within it.”

As most know, McGowan is a master of impersonation, capable of segueing from Dot Cotton to David Beckham in minutes. Cameron, however, continues to elude him. “There’s very little repetition, very little habit, very little to caricature... it’s almost suspicious.”

Listening to the 49-year-old discuss voice is a reminder that impressionism was never a party trick for him – he’s genuinely obsessed by accents, inflections, vocal tics. He’s thrilled that he’s finally nailed the tones of chef Raymond Blanc after many years of only managing an approximation of his fellow Frenchman Arsene Wenger.

“I realised quite recently that his voice comes through the top of his mouth rather than from the throat,” he says triumphantly, demonstrating his discovery with a pitch-perfect impersonation.

“It had bugged me for ages.”

When the part of phoneticist Henry Higgins came up in the 2011 West End revival of George Bernard Shaw’s Pygmalion, McGowan wasn’t even required to audition. As he puts it: “Playing a man in his 40s who’s always been interested in language and sound?

Well, that’s not much of a stretch.”

The character had made an impression decades before when the young McGowan watched the famous film adaptation My Fair Lady, which stars Audrey Hepburn as the Cockney flower girl trying to pass herself off as a lady.

“Higgins says in his opening speech, ‘I can place any man within six miles – within two miles in London and sometimes within two streets.’ When I first heard that line I thought, that’s what I want to be able to do too. It’s harder in these days of increased geographical and social mobility but accent is still a huge part of who we are and what we do.”

McGowan’s own voice is curiously featureless. He’s well-spoken, wellmoderated, but there’s little trace of his Midlands upbringing. “It comes out sometimes when I say ‘yur’ instead of ‘year’ or ‘tuth’ instead of ‘tooth’.”

The only quirk is an endearingly giggly laugh, revealed when discussing how the best character comics play versions of themselves. So Steve Coogan is really Alan Partridge, I ask?

“I couldn’t begin to say, especially not since he lives in Hove.” So that’s a yes then? Giggle.

Decades of pretending to be other people seem to have ironed out his own tones, or perhaps it’s being on stage again (he is currently reprising the role of Higgins in a touring production of the show.) “When you’re doing an impression of someone, you’re trying your utmost to sound like that person but when I’m acting I’m frequently trying not to sound like someone else,” he explains.

“There’s always someone who claims they could hear Leonard Rossiter or Billy Connolly or whoever and it’s certainly not intentional.”

McGowan trained as an actor at the Guildhall School of Music and Drama.

Prior to that he had taken an English degree at Leeds University, where he first realised his family’s habit of “doing voices” was not something everyone did. It also exposed him to the variety of accents in the UK.

“In my ignorance, I had assumed there was only London, Midlands and what they used to call North Country.”

He found work as a stand-up on graduating from Guildhall and joined Spitting Image not long after.

In his four years on the satirical ITV show, McGowan voiced puppets from John Major to sports commentator David Coleman, working alongside a roster of comics including Steve Coogan and Harry Enfield.

Parts were often inherited from the original actors: “You didn’t just have to copy the person’s voice, you had to copy the actor’s impression of someone’s voice.” To this day he is unable to accurately impersonate Newsnight presenter Jeremy Paxman – “I can only ever think of the caricatured Paxman that Steve did.”

A string of parts in TV dramas and impressions show Dead Ringers followed but it wasn’t until 2000 that McGowan became a household name through The Big Impression, the award-winning sketch show he starred in with then-girlfriend Ronni Ancona.

Launched in 2000, it ran on BBC One for four years and became one of the channel’s top-rating shows.

Although McGowan has had a good deal of success since, and starred in everything from Cabaret to Skins, he clearly misses those days. “People sometimes ask why I’m not on TV now but it’s not my decision. We did go to the BBC last year to see if the door was open to another impressions show and it clearly wasn’t. Although there seems to be a public appetite for it, there was a glut of similar shows after The Big Impression and they perhaps feels it’s all been done now.

“It’s certainly harder to put a pitch together now because viewing habits have changed so much that it’s hard to think of figures everyone is familiar with.

Everyone recognised Posh and Becks. Would everyone recognise Cara Delvingne?”

The Big Impression wasn’t without its challenges. He had broken up with Ancona – who famously played Posh to his Becks – shortly before they began filming the first series, which certainly made the subsequent four years awkward.

When the show finished he threw himself into stage work and some televised soul-searching in BBC One’s Who Do You Think You Are?

The revelation of uncovering his Anglo-Indian heritage was, he says, “a real turning point. I knew my father had been born in India but I didn’t know why. He said his parents just happened to be there. Through the programme, I found out they’d ‘just happened to be there’ since 1750.

“Finding out about my background completely changed my view of myself. It gave me confidence in my lack of confidence.

“I’d never felt like I belonged anywhere and thought it was odd that I didn’t feel a need to belong, but I realised my father – who was sort of English and sort of Indian but didn’t fit in either country – had never known or cared who he was either. It was very psychologically fulfilling.”

As he approaches 50, things seem to be ticking along rather nicely. Last year, he even broke the habit of a lifetime and got married, to fellow performer Charlotte Page, who appears in Pygmalion as his housekeeper.

Has he ever attempted an impression of his new wife, I wonder?

“Oh no,” he says. “That’s never occurred to me.

I’m not sure it would go down very well.”

* Alistair McGowan stars in Pygmalion which comes to the Theatre Royal Brighton, New Road, on Monday (March 17) and runs until March 22.

Call 0844 8717627 to book.