Maybe you know Colin Baker from Doctor Who but maybe like me, you know him from the mid 70s when he played Paul Merroney, ruthless, clever, handsome banker brought in to bail out the family business against all odds in the BBC drama series The Brothers. Either way, he is memorable, with a mellow but authoritative voice and a certain presence that makes us not a bit surprised when we learn he originally trained as a solicitor before giving it all up to tread the boards.

This month he is starring in Alan Ayckbourn’s comedy Bedroom Farce along with his chum Louise Jameson, Hannah Yelland and a host of others. We see three different bedrooms on stage, each inhabited by a couple and all have sexual, emotional and domestic problems to work out. "It’s funny," says Colin. "There’s a wonderful sardine-eating scene with Louise who plays my wife. And there’s a young couple who go round destroying everyone’s night." It’s farce at its best, complete with manic rushing around and the obligatory opening and closing of doors. It promises to be a wonderful night: Colin is very funny man indeed. So why then hasn’t he done more comedy on TV?

He ponders. "Well, I don’t know. I tend to make everything I do fairly comedic unless it’s deadly serious. When I started in this career, the very first telly part I played was a rapist, so I got stuck with playing the nasties for some time. I did a lot of costume dramas in the beginning." He has starred on TV in Moonstone, The Edwardians, Cousin Bette, War and Peace, The Roads to Freedom and Fall of Eagles. He has done a substantial number of modern dramas too: Public Eye, Dangerfield, Sunburn, Juliet Bravo, The Bill, Casualty, Doctors – and more. He’s even played a judge in Hollyoaks.

Is it strange to watch other people play the iconic part of Doctor Who? "Well, in theory it is. I suppose in practice, I’m just watching it like any other programme. It’s not my Doctor Who, any more than it was Peter’s before me, or Sylvester’s after. The doctor is mercurial. Each time it’s another character with the same name. I can either enjoy it or not, like any member of the public. It’s only when people say – that was you, wasn’t it? And I think – oh yes, so it was!"

I point out to him that some actors resent talking about roles they did years ago, especially if they attained cult status. "I know, but I don’t understand that at all," he says with a smile. "Why become an actor if you don’t want to accept that you might do something that people really like? What is the problem? I have worked with people who say, ‘I don’t want to talk about that job I did 20 years ago. I want to talk about this really tedious play about angst-ridden coal-miners in Serbo Croatia, which three people came to see last night at Tunbridge Wells. That’s what I want to talk about.’ I mean, get a life! I feel lucky to be in a job where people can look back and praise me for work I did. If you’re a shop-fitter, no-one says to you, ‘That Tesco you did in 1983, what a cracker!’ Some actors let their egos take over their lives to an alarming degree."

Some of the stalwart Doctor Who fans bring Colin down to earth with a bump. "They can be very forthright, you know. They come up to you and say, ‘You’re my fifth favourite doctor.’ Or: ‘All my friends hate your doctor, but I quite like you.’ On the other hand, now and again, someone will say I’m their favourite doctor. Out there, there’s a whole swathe of opinion about everybody. There must be some who hate Tom Baker’s doctor; I’ve never met one, but there might be somebody."

His background is embedded firmly in south west London. "I was born on Waterloo Bridge," he says. "The Royal Waterloo Lying-in Hospital on the south end – in the middle of an air raid. My mother was born in Stockwell and my father in Tooting – and they were living in Balham High Road and I spent my childhood there. Years later, when I was in my late teens, my father died and we moved to Clapham Park, as we called it. It was very genteel then – semi-detached houses, my dear." I point out that Noel Coward grew up in Clapham. "Did he? I didn’t know. And there the similarity ends."

In his early 20s, Colin went to LAMDA to study drama. "I used to cycle across Clapham Common, down through Battersea and over the bridge, through Chelsea and up to Brompton Road. You couldn’t do that now – you’d be dead in minutes. I suppose traffic is one of the biggest changes since those days in the 60s. When I was living in Clapham then, I knew exactly how long it took me to drive to my friend’s house in Clapton, in the East End. You had to be careful not to break the speed limit. Now, you don’t worry about that because if you go more than five miles an hour, you’re doing very well. It can take 40 minutes or it can take two hours."

Is it sad to see the area so changed? "I suppose it’s depressing because we all want things to be the same as we remember them. That’s entirely unrealistic, but I sometimes feel they shouldn’t mess with my memories. There’s nothing wrong with being sorry things have changed. It’s a lesson we all have to learn. Time moves on. Inside my head, I’m still playing young men on TV. I’m still in my 20s, cycling across Clapham Common."

Colin Baker is starring in Bedroom Farce at Richmond Theatre 25-30 June (box office 0870 060 6651)