Peter Byrne definitely knows his Agatha Christie. How could he not, after stints directing and starring in The Mousetrap, the longest running play in the world at 23,000 performances and counting?

And if that were not enough, the Dixon of Dock Green actor is now appearing in another Christie record-breaker, And Then There Were None, whose 100 million copies make it the best-selling mystery novel of all time.

The classic whodunnit sees ten people trapped on an island in Devon with the mysterious Mr U N Owen (geddit?) and one-by-one bumped off to the lines of that old nursery rhyme, Ten Little Indians.

Byrne plays war hero, General Macarthur, who like all the characters has secrets to hide. He stars opposite fellow TV faces Gerald Harper, Alex Ferns and Chloe Newsome.

"People tend to poo-poo Agatha Christie," says Byrne. "But there's much more to her than people think. As a play, I'd say this one ranks up there with Witness for the Prosecution. It's sold out everywhere we've gone so far."

Currently ensconced at the Wolverhampton Grand, Byrne is busy writing thank you letters in his hotel room when I call. Last month, he turned 80 and his wife Renee threw him a big surprise birthday party at home in Hendon - cue lots of presents from family and friends.

If the octogenarian is slowing down, he shows no signs of it, even if, as he jokes, "I seem to have cornered the market on TV for angina sufferers."

Still best known as Andy Crawford in Dixon (a part recently revived on radio by David Tennant of Doctor Who fame), Byrne's recent TV roles include patients on Holby City and Doctors, and aging Tony Blair in Armando Iannuci's satire Time Trumpets. "One of my more demented parts," he says with a chuckle.

But theatre feels like home. Byrne trained at Itali Conti before the war shut down the school and packed him off to the army.

Returning to rep seasons in Farnham, Nottingham, Windsor and Worthing, he met Jack Warner and was cast in Dixon.

The programme aired soon after the Queen's Coronation and many families had just bought their very first 8 inch television sets.

For Byrne, at least, it was television's Golden Era: "There was just one channel which paid very poorly so to start with, established actors didn't want to know and actors like myself, coming out of rep, had the pick of the parts.

"It was a wonderful time, rather like the early days of Hollywood, I like to imagine.

"We did 155 live programmes and when you made your mistakes, you made them in front of 15 million people. But I always enjoyed live TV - I'm a bit of gambler and to me it seemed more like theatre."

Agatha Christie demands a similar team spirit. "There's a surprising amount of humour," says Byrne. "I think she does it deliberately, just before something ghastly is going to happen, so there's a release of air before you are suddenly on the edge of your seat again. But it means you have to be very tight as a cast."

And Then There Were None, Richmond Theatre, The Green, Richmond, Monday, February 18 to Saturday, February 23, 7.45pm, Wed/Sat mat 2.30pm, £14-£26, call 0870 060 6651, visit richmondtheatre.net.