As barman Kev in the Channel 4 comedy Shameless, Dean Lennox Kelly became one of the coolest men on TV. Now the Brighton actor is bringing his laid-back charm to the role of Shakespeare for the most expensive episode ever of Dr Who. He talks to Bella Todd about tackling monsters, on-screen masturbation and Diego Maradona.

Basically it's about these witches. Carrionites. Or are they Plasmavores? They've got broomsticks and they use words to create powerful magic and dark destruction. And they have a voodoo doll of me, Shakespeare, and they make me write a play. Basically they're conjuring spirits and bad things, alien life forces..." Dean Lennox Kelly pauses, runs his fingers through his newly-acquired beard.

"I'm gonna have to possibly ring you about the plot."

Best known for playing laid-back barman Kev in the first three series of Channel 4's Shameless, the Brighton actor is currently sat in his local boozer, The Lion & Lobster, trying valiantly to summarise the plot of tonight's episode of Dr Who.

Described by director Phil Collinson as "the most expensive episode ever", the second instalment in the new series is one of the most anticipated in Dr Who history. Set in 1599, The Shakespeare Code reportedly sees the Doctor (David Tennant) travel back to Tudor London in order to prove to new recruit Martha Jones (Freema Agyeman) that the Tardis is a time machine. Here they encounter William Shakespeare (Kelly), who has to give the performance of his life in order to save the Earth from destruction by forces from the dawn of the universe.

There has also been some unofficial talk of "blood-sucking alien Plasmavores"

in this episode, but here even the fans seem to be as clueless as Kelly. "This may sound silly," hesitates one forum visitor, "but what are the Plasmavores?" "I think," speculates another poster, "they might eat plasma."

Kelly is neither a fan of Dr Who nor a fan of the Bard. His first foray into Shakespeare was A Midsummer Night's Dream, part of the BBC's 2005 ShakespeaRe-Told season, in which he played Puck as a sort of magical wide boy. His brother, Craig Kelly, played the Dr Who fan Vince Tyler in Channel 4 drama Queer As Folk - also written by Dr Who's producer Russell T Davies. But Daleks never registered in the Kelly boys' childhood.

Actually, this makes the 32 year old the perfect guest star for a revival, now into its third series, whose winning ingredient has been the tone of comically outraged normality. It also makes Kelly a clever bet to portray Shakespeare for a teatime audience.

"I'm not the obvious choice to play Shakespeare," he says, supping on a half of Guinness in scuffed jeans and a leather jacket. "But they didn't want your archetypal Shakespeare. They wanted him to be more like a 15thcentury rock star. The director kept saying to me, Think Liam Gallagher with lyrical genius.' "

Kelly was so sold on the idea of the world's most famous playwright being a "man of the people" that he tried, unsuccessfully, to include a line in which Shakespeare insists on being called Bill.

He grew a beard, made the most of his chest hair ("I love that people think I had a chest wig in Shameless - it's all mine!") and revelled in a "slightly Pirates of the Caribbean" costume which encouraged him to overcome a natural fear of breeches. "Is that what they call those puffy trousers? Yeah, breeches. I tend to avoid them because my legs are quite short and you can look a bit dumpy."

Featuring 3,000 extras (that's 200 paid actors multiplied with the magic of CGI), The Shakespeare Code was filmed on location in Coventry and Warwick in pursuit of authentic Elizabethan streets.

Although close-ups were shot using replicas of the theatre, the crew spent three nights in the Globe on London's South Bank. Two weeks prior to filming, Kelly visited it for the first time, to see his mate Cal MacAninch (with whom he starred in 2006 BBC drama Sorted) play Long John Silver in Under the Black Flag. But the force of the Globe's history only struck him when he took to its boards himself.

"It's amazing, and quite eerie," he says. "Although they rebuilt it, it's on exactly the same spot as Shakespeare's Globe, which was quite overwhelming. I didn't really think about it until the bit where the crowd start shouting Shakespeare, Shakespeare! Author, author!' and I have to walk out on to the stage blowing kisses. In the script it actually says, Shakespeare arrives like a rock star.' It was like, oh my god, I'm Shakespeare on the Globe stage."

Such was the credibility of his character in Shameless, a comedy drama set on a Manchester council estate, Kelly has become something of a professional working class Northerner. Sorted, his first job after leaving Shameless in 2006, was about a group of Manchester postmen.

Dead Clever, a black comedy which aired on New Year's Day, was set in North Yorkshire and saw him play a drunken, philandering husband.

He is about to start filming The Cranford Chronicles, a five-part serial based on the novels by 19th-century Mancunian writer Elizabeth Gaskell.

He will play a father of eight and star alongside Judi Dench.

In fact, Kelly grew up in Lytham St Annes, a seaside resort near Blackpool which he describes as "a posh little town where we got out of the bath to go for a wee". The double-barrelled name isn't real, mind: he added Lennox, his mother's maiden name, after turning up to numerous voice-over jobs to be told he was "the wrong Dean Kelly".

"The other Dean Kelly is a children's entertainer, specialising in finger puppets,"

he says. "I met him at a wedding once. We didn't get on too well."

Kelly's first acting experience was the school nativity, aged seven. He had secured the part of Shepherd, but botched it by dropping his sheep as he was due to go on stage. "I was crying before I even entered," he remembers.

"Totally lost it."

Eight or so years later there followed a job at Blackpool's now defunct Elvis Presley Centre. "Nobody believed it, basically, that's why it didn't work," he says of this rather bizarre tourist attraction.

"Nobody could believe someone would put Elvis's real discs and karate suits and combs inside this place in Blackpool."

Kelly would be on the door with a mic and a "Taking Care of Business" tie, singing snatches of Love Me Tender and inviting tourists to "walk right through the gates of Graceland!" His mates would be hovering across the road, taking the piss. He still has the tie.

For a time, Kelly tried his luck as a stand-up comedian. I ask him to tell me a joke and he leans into the Dictaphone, low voice, serious expression: "Two flies on a piece of sh*t" He loved the immediacy of the crowd, the laughs, but he couldn't write his own material. "I went to Corfu when I was 17 and worked the bars, and when I came back I was on the dole. I realised, if I went to drama school, that was the next three years covered."

Kelly maintains that what he learnt at Bristol Old Vic Theatre School, and what he went in with, were one and the same thing. "All you've got as an actor is your instinct," he says. "That's what gets you work, not technique'." But it was here that he met his good friend Richard Coyle (Jeff Murdock in Coupling), the two trainee actors bonding when they both got bum roles in the end-of-year performance. The play was The Grapes of Wrath: Coyle was cast as the 85-year-old granddad, Kelly the drunken old uncle.

The pair share a mischievous sense of humour, and recently furnished The Independent's How We Met section with a heart-warming interview in which Kelly told the journalist, "When we hug we hold each other longer than we should". When Coyle married fellow actor Georgia Mackenzie in 2004, Kelly was best man "I've been best man four times,"

he says. "I like to get up and tell some gags. It's the best audience you'll ever play to. I like to get up, wait for everyone to go really quiet, maybe take a drink, then take the mic and, absolutely deadpan, go, I give it six months'."

Kevin "Kev" Ball, Kelly's character through three series of Shameless, typified everybody's idea of what a best man should be. Married to the peroxide blonde loud-mouth Veronica, he was solid, warm-hearted and up for a party, whether he was nicking the council's Diana Memorial Garden for his girlfriend, encouraging the local tart-with-a-heart to "cheer up" Fiona's ex in the bogs or proudly unveiling a drinks cabinet tackily disguised as a beer barrel.

One style section even decided that Kelly, as Kev, was "the coolest man on television". "He's funny, tough, charming," wrote GQ editor Dylan Jones, "and has the sort of Jack-the-Lad councilhouse insouciance that looks as though it body-swerved the Nineties lad culture completely, reminding one more of Adam Faith's Budgie, back in the Seventies."

"What's great about Kev is he's one of them characters that the lads liked and the girls liked," says Kelly. "When I first moved to Brighton I had lots of people coming up to me going, Kev man, all right mate?' There's a big part of me in Kev: the chest hair and the football. I quite liked his clothes, too.

I used to sneak some of my own stuff on - all those nice retro Seventies Adidas tops were mine.

"But I like good food and good wine, and I like a facepack now and again - I'll borrow my mum's or my girlfriend's.

If you've been out or you feel like sh*t, I like the feel of the mud tightening on yer face. That's not very Kev."

Kelly hadn't worked for 15 months when he took the Shameless job, and had no idea how successful the programme would prove.

"I knew it was well written but when you're making something, you can't tell how it's coming across," he says. "What was amazing about Shameless was there was no division in the audience.

Every one seemed to watch it - because the heart of it is family, and everyone's got mad family."

Sex in all its boldest manifestations, from alleyway knee shakers to pirated home videos, is also integral to the programme's brand of gritty comedy.

And Kelly was charged with setting the tone in the very first episode, lying stark naked on faux leopardskin sheets with his legs at 20 to four.

"That was definitely the most embarrassing moment," he laughs. It was a very cold day and there were five people in the room, all of them men. There was another bad episode at the start of the second series when Kev had a crush on his reading teacher and I had to pretend to masturbate a few times on camera. That was really embarrassing 'cos it was a female director and she was kind of giving me notes about what my position should be like. Trust me, lady, I'm doing it right."

In the end, Kelly reckons, it was OK because Kev and Veronica's sex scenes were all comic. "If I had to try and be seriously sexy - soft music and panning camera shots - I'd be mortified."

But he's not sure we'll be seeing quite so much of the Kelly physique in future.

"If the script was good enough, I think I would consider keeping my clothes on," he jokes. To be honest, I'm past 30 now, and I'm getting to the point where I'm a bit more worried about what I look like. My girlfriend's brilliant about it but basically you don't want to see the person you love and have a baby with knocking one off on telly."

Eugenie Rose Garrett, with whom Kelly had a son five months ago, is the singer with a great fledgling folk group called Rosewood Green. Kelly is a massive music fan, who last year entertained an Observer journalist at this same Brighton pub with a pile of cherished old vinyl and a Seventiesstyle portable record player. His favourites are soul singers - Ray Charles, Terry Callier, Marvin Gaye - but Garrett has got him into Bob Dylan and Joan Baez.

They have a campervan in which they take off to music festivals when Kelly gets a break from filming. He has a Fender acoustic but claims his repertoire consists solely of Let it Be.

Kelly and Garrett first met in a pub in London, before Kelly fled the capital for the coast three years ago. The pub was packed with people watching Manchester United play Arsenal, and the actor's attention was caught by the sight of a lone woman who seemed to have no interest in the game whatsoever. "I just saw all these blokes watching the telly, and this one woman looking the other way," he says.

"That was it."

Never one to romanticise the acting profession, these days, with a five-month-old son to support, Kelly says his work feels "more like a job than ever". He has just been up to London to record the voiceover for something called The Real Dirty Dancing, opening line: "Can you teach someone to be sexy?"

He is not particularly excited about beginning work with Judi Dench, who he imagines "must be a bit embarrassed by the way she gets nominated for awards whatever she does".

His biggest upcoming project is Frequently Asked Questions About Time Travel, which he has been filming at Pinewood Studios with American Scary Movie actor Anna Faris, The IT Crowd's Chris O'Dowd and Shirley Ghostman's Marc Woottan. Directed by Gareth Carrivick, it's a sci-fi comedy ("I only take work at the moment if there are monsters") penned by writer and comedian Jamie Mathieson "in response" to Shaun of the Dead.

Kelly does a better job of relaying the plot on this one. "It's about two geeks and a cynic who find a time loop in the toilet in their local pub, and there's bad sh*t going on." But he brightens considerably when I stop trying to nail the exact nature of this bad sh*t and ask him, instead, about Soccer Aid.

A lifelong Liverpool fan, as a child Kelly had hopes of becoming a professional footballer. He was eventually invited to play one, in the 2001 satirical film comedy Mike Bassett: England Manager but unfortunately, the player in question was a washedup alcoholic more prone to streaking than scoring.

His dream's came true, however, when he took part in ITV's Soccer Aid, a charity event held in May last year which raised £3 million for UNICEF.

Initiated by Robbie Williams and presenter Jonathan Wilkes, it saw two teams comprising celebrities and World Cup legends take each other on under the titles of England and Rest of the World.

"I rang up Max Beasley, who's a mate of mine and a mate of Robbie Williams, and begged to be on it," says Kelly. "I think I only got on it 'cos Gareth Gates dropped out. I only had four weeks to get fit and I hadn't been on a full-size pitch since I was 19. I was driving up to the Downs and running every morning, in among the sheep."

Playing in midfield for Terry Venables' England team alongside the likes of Paul Gascoigne, Jamie Redknapp and David Seaman (not to mention Angus Deayton, Jamie Theakston and David Gray), Kelly earned himself Man of the Match in the warm-up game. When it came to the real match, at Old Trafford, playing in front of a crowd of 74,000, the adrenaline buzz was immense.

"We were all standing in the tunnel waiting to run on - Seaman's there, Gascoigne, Le Saux - and suddenly David Gray just started singing at the top of his voice," laughs Kelly. "He wasn't really singing anything particular, just going wa-aaah, wo-aaah' there in the tunnel. I was like, All right Dave?' He was just dealing with his nerves, y'know?"

In the end, the England team won 2-1, a result Kelly would like to have me believe they celebrated "by getting in the showers together in the nud, passing champagne around and slapping each other's buttocks". His personal moment of glory came later, back home in Brighton, when he watched back the tape of the game.

"There's a bit on the commentary where the commentator says, Maradona on the halfway line... Oh, and Kelly takes the ball off Maradona!' " he tells me. "I've sat and rewound that little moment so many times. In my career there isn't a greater moment than that. I don't mean my life, obviously, 'cos that's me and my girlfriend and our baby.

But careerwise, nothing tops it. Not even playing Shakespeare."