"My character, fire-fighter Sally `Gracie' Fields, gets raped and tries to wash away what has happened to her by scrubbing herself clean in the shower," explains Heather, 25.

"Originally, she was just going to sit on a sofa in the foetal position, too scared and traumatised to move an inch. But I thought that was a bit weak and suggested I did the shower scene. I thought there ought to be a more graphic and powerful reminder of what had happened to her.

"I wanted to show her fighting what she'd been through, fighting to eliminate every last trace of this guy's attack. And because Sally has suffered the most horrifying and humiliating ordeal of her life, I knew I had no choice but to bare all, however much I might have resisted doing so in the past. Or virtually all... I did keep my G-string on and there was probably enough steam in the shower cubicle when we filmed to make sure some parts of me were hidden from view."

Following a night out, Sally is raped by Watch Commander Sean Bateman (played by Dominic Taylor) in one of the most harrowing storylines ever tackled by ITV's fire-fighting drama.

"Not only has Sally been attacked at a time when she is looking for comfort and love following the death of her lover Joe, but Bateman then denies rape, claiming that Sally consented to sex," adds Heather. "So she faces an agonising battle to prove his guilt."

Heather, who lives in Brighton with her partner, had no qualms about taking on such an emotive and disturbing storyline.

"From a purely cosmetic point of view, I felt the need to lose a bit of weight because going naked does make you feel very self-conscious. So I cut back on the pints of lager a bit," she says. "But this is a story that needs telling. A horrifying number of women are raped by men who they know, often in date-rape circumstances, and this problem needs highlighting."

Sadly, Heather did not have to go too far to research her part. "I've never been raped - the worst thing that happened to me was being flashed at in a park when I was growing up in Bradford, and that was a pretty disturbing experience," she says. "But a close friend of mine was attacked under similar circumstances to Sally. She was on a date and the guy raped her.

"I knew what had happened to her when the storyline was first mentioned, so I knew there was somebody who I could talk to about what Sally goes through, as long as my friend felt all right about talking. I wouldn't have asked her had I thought it was going to cause her distress."

Heather adds, "As it was, she went into great detail and the overwhelming feeling she had after the rape was not anger or pain, but exhaustion. She said she cried like a child would when they can't get their breath because all the energy has gone from their bodies. A lot of what she said to me I've tried to include in my portrayal."

Viewers will see none of the rape, just the moments leading up to it and the aftermath. This ordeal, on top of Sally`s grief at the death of her boyfriend Joe in a blaze, means Heather has spent long periods in tears for this latest series.

"Luckily, I don't take my work home and far from being upset by the rape I thought, `I'm exhausted, but I've just had one of the best days of my working life'. That scene was the most challenging thing I've ever had to do, but also the most fulfilling. It certainly beats playing a professional extra, which is what I am most of the time in London's Burning."

That last comment indicates a degree of disillusionment with the top-rated show, and it seems almost certain that Heather will quit when the current series ends.

"I don't want to spend the whole of my twenties in one programme, however good a bunch of people they are to work with and however good the show is," she says. "And they are good people and it is a good show. I want to travel more, do some more theatre and do more TV. I'll have done three series of London's Burning by the time this one ends, and that, I think, is probably enough."

Whatever she decides to do next, making another record is not high on her list. Heather was a professional jazz singer before joining the show and released a cover of the Bette Midler number The Rose during her second series, but she is not keen to get back in the recording studio.

"I was full of enthusiasm when I released The Rose and there was a real buzz about me doing it, but I wouldn't want to go down that route again," she says. "Having been in and around the music business I've seen how cutthroat it can be and it's not something I really want to be a part of again.

"I still like singing, but I think, in future, I will stick to small- scale jazz gigs like the ones I used to do in Manchester when I was part of a duo called Heather And Steve.

"I don't really want to say too much about The Rose but the single didn't do that well and the album I was hoping would follow it didn't materialise. Basically, I was disappointed with the way things went and the way it was all handled. And while I don't regret doing it, it's not an experience I'm keen to repeat."

After everything her character has suffered, Heather is hoping that Sally will be written out of the series on a positive note.

"She's been mugged, raped and lost her boyfriend in a fire, so I've told the scriptwriters that I don't think it would be fair if she were killed off while fighting a blaze or if she were to die in similarly tragic circumstances.

"I hope she'll get a really good send-off - a promotion to another station or something like that would be great."