My Family, one of TV's most popular shows, picks up audiences of millions every week.

But for its star Robert Lindsay, nothing can compare with the very different satisfactions that the theatre has to offer.

Robert's small-screen successes are legendary, going right back to the iconic urban revolutionary Wolfie Smith in the 1970s.

But the theatre is where his heart is.

He's now starring in Chichester's Minerva theatre in Martin Sherman's new play Aristo, the story of the last years in the life of Aristotle Onassis, and of his complex and interwoven relationships with Jackie Kennedy and Maria Callas.

"Theatre is what I do best," Robert says. "It's where I function best. It's just in my latter years I couldn't afford to commit to the kind of length of run that producers were wanting.

"The only living for actors is either a huge long run in something or TV or movies. I have actually done a lot of films, but not many of them have seen the light of day. Films are very volatile. It's a very strange world. And it's not really my world. My world is the theatre.

"My wife is wonderful. She knows what I miss about it. It's where I have done my best work without doubt. I feel at one in the space in a theatre. I don't feel threatened.

"And I feel that the audience get the full benefit of it. It is not edited. It is not changed in anyway. You get what you pay for, and I love the event feeling of it. It's something we have got to hold on to. We are just losing each other otherwise. We are just getting isolated.

"A lot of TV work is really just to keep me ticking over. Like anything it becomes routine."

Rather more than that, though, is My Family, one of the country's best-loved TV series over the past nine years.

"Nine years! Who would have thought it would have lasted nine years. The press hated it because it is a domestic comedy, but it is actually one of the most popular shows on TV.

"It's not easy for a bunch of sophisticated actors! We have got grown-up agendas. It's very hard to keep within the watershed. We have got to make it tasteful.

"It has picked up a huge audience – children of all ages. The mail that you get from that show is unprecedented. I get a lot of letters from a (particular) little boy who pleads with me to be a member of the family because he thinks we have such fun."

Whether that makes it a sitcom, though, is another matter. Robert thinks not: "It's more a sketch show. None of the stories link. It's about what happens when parents say the things they should not say, but they are still tiny sketches."

"With something like My Family, it's like Eric and Hattie, it's like Terry and June. They are part of our culture, this whacky middle-class family in Chiswick.

"There are obviously a wealthy family in a five-bedroom house in Chiswick. We are talking about a £2.5 million house, and that's what people find attractive – the fact that they live in this expensive house and yet they act like any other family.

"They keep asking us. Zoe (Wanamaker who plays his wife) and myself have got so many other things that we want to do. If they got their wicked way with us, they would tie us down for a long time. But we are still up for grabs. We enjoy it. That's the point. We have a lot of fun, but then when you get your teeth into something like this (Aristo) you realise that your muscles are not being stretched."

In My Family, Robert concedes, there is just an element of treading water: "We do what we do best. We do feel comfortable. But then it's a comfortable show. We are not trying to change the world."

Just what Wolfie Smith would make of that last statement is anybody's guess. Wolfie, is – or was – of course the hero of the classic 70s sitcom Citizen Smith, one of Robert's earliest high-profile roles.

"I think that that would have lasted a lot longer if I had not been so young and wanted to go off and do theatre. Everyone was devastated when I said 'I am a serious actor'. I pulled the plug on it, but at that point we were picking up 14 or 15 million viewers. We did three series with it. I think it was only 21 episodes."

The Greek play

As for Aristo, the task in hand at the moment, Robert is relishing the challenges it is throwing up.

"It's just overwhelmingly exciting. The script, the venue, the production, the subject matter… It will be interesting to see what the folk of Chichester think. We know that it is a very theatrical community. It's the perfect venue to try this."

What appeals is the "sheer power of the character, the overwhelming greed and hunger of the man, not only for money but also for life".

"Those kind of people fascinate me because you know there are weaknesses, and those weaknesses will become apparent.

"It's a Greek play. It's the fact that these people are gods, believe they are gods. They were so famous it was unreal. They were the last of the major celebrities, and they behaved accordingly.

"I have read an awful lot about the character. When he entertained on his yacht, people said that you were at the centre of the earth. The people there were people like Winston Churchill, Jackie Kennedy, Hemmingway…

"In business there is no such thing as moral scruples. We are talking about people determined to go to any length to get what they wanted."

Robert Maxwell is an obvious parallel. Mohammed Al Fayed is too, Robert suggests: "But all these people will pay a price. Onassis paid a great price. He lost his son who was assassinated. All great plays have this element of everyone paying a price."

* Aristo, CFT, until October 11, and sold out before the run began. Only returns now available.