IT’S MORE than 15 years since Gwyneth Strong last appeared in the TV sitcom Only Fools and Horses but she knows she’ll always be known as Cassandra, and doesn’t seem to mind a bit.

“I don’t think any of us thought it would be as huge as it was, but of course when I went into the sitcom it was already a successful comedy show, so I had an idea, but I didn’t realise that it would just get bigger and bigger,” she says, recalling her role as the love interest for the hapless Rodney Trotter.

“I’d been acting for a long time before playing Cassandra, and I’d been in television shows so I’d experienced some recognition every now and again, but absolutely nothing on this scale! It changed everything really.

“The feeling towards that programme and that character; the sentiment is so generous and so loved that you can’t really feel anything but happy that people are still so fond of Only Fools and Horses. The warmth that people bring when they want to say something about it is lovely and I’m very lucky to have been in a show like that.”

Now aged 59, Gwyneth is turning her attention to the stage and a very different character,  the formidable Mrs Boyle in Agatha Christie’s record-breaking stage phenomenon, The Mousetrap.

The play is celebrated for being the world’s longest-running show of any kind in the history of theatre, and Gwyneth says: “It’s really exciting to be part of something that has a historical background like this. You know you’re becoming part of a cannon of actresses that have played the role and I think that shows real trust; it’s lovely.

“I really am looking forward to getting back on stage. I love theatre and I don’t like to leave it too long because it’s like a muscle that you need to use. I really like being part of a company and being on stage in front of an audience, once I’ve got over my nerves and into in my stride. I love it.

“I’ve never done any Agatha Christie so I really fancied doing that style of theatre and I was very attracted to the character, Mrs Boyle. She’s very bombastic and angry, and as an actress I was drawn to having a go at taking on a role like this. I haven’t played an angry character in a period piece before, so it will be a brilliant new challenge for me.”

The Mousetrap is the story of a group of people gathered in a country house cut off by the snow, only to discover that there is a murderer in their midst. One by one, the suspicious characters reveal their sordid pasts until, at the last moment, the identity and the motive of the killer are finally revealed.

Gwyneth, who was born in London, says it has made her a big Christie fan, explaining: “I hadn’t read or seen The Mousetrap, and when I settled myself down to read the script, I was supposed to be phoning somebody back and I completely forgot. I became so immersed in the story, I just carried on reading right through to the end. I was completely sucked in and I think that must be what happens to audiences. The story consumes you.” Gwyneth Strong will be joined on stage by David Alcock (Mr Paravacini), Geoff Arnold (Detective Sgt Trotter), Nick Biadon (Giles Ralston), Lewis Chandler (Christopher Wren), John Griffiths (Major Metcalf), Harriett Hare (Mollie Ralston) and Saskia Vaigncourt-Strallen (Miss Caswell).

The Mousetrap will run at the Yvonne Arnaud Theatre, Guildford, from Tuesday 29 January until Saturday 2 February.