JEMMA Walker smiles at the thought of how her demure role contrasts with her past performances.

“For once I have no short skirt or stilettos this time. It’s nice to be playing against type as someone posh and fully clothed,” says Jemma, who is appearing as Mollie Ralston, co-owner of the country house guest house where Agatha Christie’s venerable thriller, The Mousetrap, is set.

Yes, that play, the one that has been running unbroken on the London stage since opening at The Ambassadors Theatre in 1952 with a cast led by Richard Attenborough and his wife, Sheila Sim.

The play had warmed up for London with regional performances that included a run at the Leeds Grand Theatre, where Jemma was interviewed on The Mousetrap’s return there in March during the 60th anniversary tour.

“It’s a pleasure to be in the show because it’s the first ever tour and it’s got a super group of people together in the cast [Bruno Langley, Karl Howman and Graham Seed among them] – and it’s great to be part of something so prestigious,” says Jemma, who has been on the road since last September and will continue in her role until June.

You may recall Jemma from her television roles as Sasha Perkins in EastEnders and Siobhan Jones in Family Affairs, or her blonde bombshell stage appearances for Hull Truck Theatre in Amanda Whittington’s brace of plays Ladies Day and Ladies Day Down Under in 2005 and 2006.

“Jemma Walker’s spectacular Shelley, a brittle and brassy wannabe celebrity, makes Footballers Wives look like the bastions of good taste,” wrote The Press.

She has happy memories of those plays. “You can tell on stage when people really get on and we’ve all become best friends from those shows,” she says.

“I think that was testament to Amanda’s great writing for women and Gareth Tudor Price really understood it with his direction. It all just clicked; it was the best job of my life – and I found my Australian husband from it.”

Jemma is greatly enjoying The Mousetrap too, especially the experience of working with director Ian Watt-Smith, who directed the murder mystery’s 38th, 41st, 58th and 59th years at the St Martin’s Theatre and a production at the Vasa Theatre, Stockholm.

“He’s done it a number of times and I think that’s why they’ve asked him to do the Diamond Anniversary Tour,” says Jemma. “His opening advice to us was to serve what Agatha Christie wrote as, at the end of the day, it’s stood the test of time.

“We had three weeks of rehearsals in London and after we did a read-through web got stuck in straightaway. There’s a lot of text, a lot of back story and a lot of red herrings. It’s a whodunit with a lot of discussions going on – and lots of doors to remember which one you should be using at any one moment. It can get confusing after a while.”

Analysing Christie’s 60-year-old dialogue, Jemma says: “Some people call this play a museum piece, but I don’t know if that’s quite true, though it is particular to that period and the language does sound dated because it’s not naturalistic.

“You can’t go against that when you’re playing it. You have to play it faithfully. I know for a fact – because I’m on stage with all the other actors – that none of us is sending it up. If you want to send it up, go and do Tom Stoppard’s The Real Inspector Hound.”

The Mousetrap may be closing in on retirement age but shows no sign of exiting stage left. “Not even Agatha Christie expected it to last more than a year but it started a genre of whodunits, and because it’s the original and where it all began, people still want to see it,” says Jemma.

“It’s because of The Mousetrap that we’re now used to going to plays with a sixth sense when they have a whodunit plot and a trick ending.”

• The Diamond Anniversary Tour of Agatha Christie’s The Mousetrap runs at Grand Opera House, York, from May 6 to 11 at 7.30pm plus 2.30pm, Wednesday and Saturday. Box office: 0844 871 3024 or atgtickets.com/york