Stephanie Lawrence, Clodagh Rodgers, Kiki Dee, Lyn Paul and four of the Nolan sisters (Linda, Bernie, Denise and Maureen) have all played the central character in Willy Russell's cult musical Blood Brothers.

Now it's Marti Webb's turn (Mayflower Theatre, Southampton, October 6-18).

"(Producer) Bill Kenwright has been trying to get me to do it for years," says Marti. "Now he has succeeded. It's just a fluke that I was free to do it. It was very much a fluke. Linda was taken ill. Linda was supposed to be doing this part, and I just stepped in."

Usually she'd expect at least two to three weeks' rehearsal. Marti took over after just a week and a half.

"But fortunately it's such a fantastic story," Marti says. "It has got such a wonderful storyline."

It inspires the performers every bit as much as it inspires its audiences: "It's just so moving. I am usually uncontrollable by the end."

Telling the story of twin boys separated at birth, only to be re-united by a twist of fate and a mother's haunting secret, the musical comes charged with emotion – plus a score which includes A Bright New Day, Marilyn Monroe and Tell Me It's Not True.

"The whole thing is a journey for Mrs Johnstone. She starts off very young and by the end she is very world-weary."

The key to the show's success is that she comes across as such a real person, someone everyone can identify with: "She is just an ordinary woman in extraordinary circumstances. The world takes her over. And the ending is just so sad.

"The script is so good, and the songs are just so seamless with the script. Every one of them tells a story."

For Marti, it's the latest in a remarkable string of key roles in the nation's best-loved musicals. Past credits include Stop the World I Want to Get Off; Half a Sixpence; Oliver!; Godspell; The Card; The Good Companion; Evita; Cats; The Seven Deadly Sins for The English National Opera and Thoroughly Modern Millie playing Mrs Meers.

Understandably, though, she declines to compare and contrast Mrs Johnstone with the roles that have gone before. Each one stands alone.

"I think I have just been very lucky. Some people would say it is talent, but luck does come into it. It really is also about being in the right place at the right time. These parts really are few and far between. There are few good parts for women."

And Mrs Johnstone is certainly one of them: "It's a very enjoyable experience. Everybody works so hard. We all get on well and it is just fabulous to do."

Tickets for Southampon on 02380 711811 or online at mayflower.org.uk.