Hidden away behind a disused warehouse in London's bustling East End, a modest caravan is providing welcome rest and recuperation for The Royle Family star Sue Johnston.

Johnston, who can be seen in the new BBC two part thriller Waking The Dead in which she plays a psychological profiler, is resting up after damaging the tendons in her leg an accident which occurred during filming.

During rehearsals for the police series, the actress was dashing to an all-action, riverside shot when she slipped and fell. Despite the obvious discomfort the accident has caused her, she smiles when she recalls the ambulance's arrival.

Paramedics turned up to find Johnston being comforted by her co-star Claire Goose, better known for her role as a TV nurse in BBC's Casualty, but dressed for her new role Detective Constable Mel Silver. I'm a Casualty fan and I thought it was funny, even while I lay there, Johnston grins.

However the resulting injury has seen Johnston laid up ever since not that it is all bad news, while recuperating the actress has taken the opportunity of indulging in nostalgia by watching the Brookside omnibus.

I still like to keep up with what's going on from time to time, admits the 56-year-old. Brookside was a big chunk of my life.

The accident was an unfortunate blip in the making of a drama that gives Johnston the chance to show, yet again, just what a chameleon character actress she can be.

Made between series of The Royle Family, in which she plays the downtrodden Barbara, her role as Dr Grace Foley could hardly be more different.

Isn't it great, I get to go tearing round in police cars, looking clever, she beams, although she admits the role didn't give her a chance to display her more glamorous side.

Grace's wardrobe is only a bit more exciting than Barbara's, she explains. I wanted her to be the kind of woman who is really not interested in the way she looks. Working with these beautiful women in the team, she has to look quite plain, just a workaholic. Her job takes up all her energy and her time, clothes are the last thing on her mind.

But Johnston did have to steel herself for playing out the realities of Dr Foley's day to day job seeing the gruesome images of the victims of violent crime.

Psychological profilers will all carry pictures in their heads of what their eyes have seen, she says. Even after years and years working with the police force, it can all still be there.

For me it was seeing case histories of real crimes. I knew I wasn't taking it in. I had to keep saying to myself, 'This isn't just a good make-up job, this is a real person'. The instinct is to recoil, but people like Grace have to face these things.

Waking The Dead also stars Trevor Eve as the head of a newly formed 'cold case' squad, a team which deals with everything from police procedure and detection to forensics and criminal psychology.

A five-year-old murder case is re-activated when another young girl is abducted and time is rapidly running out as the team try and track down the man responsible before he kills again. I confess I was a bit sceptical at first as to whether people like Grace could really be of use, says Johnston. But they have really proved their worth, especially when they are brought in right at the beginning of a case.

I met a Scotland Yard analyst and found what she did totally fascinating. In most cases, how you are treated in childhood can affect you for the rest of your life. But not everyone turns out to be a psychopath or a sexual deviant thank God!

Warrington-born Johnston has had to wait a long time to get the recognition she so richly deserves and she still cannot quite believe that it was a one-set comedy that has brought her such critical acclaim.

Although thanks to The Royle Family and her earlier Brookside role, Johnston is seen as the archetypical matriarch, she is herself a single mother with a grown-up son, not that she is bothered by the inevitable comparisons between herself and Barbara Royle. As an actor it is always fascinating to dive into a character and that's what I do, she says simply. I always thought The Royle Family was hysterically funny when I got the scripts, but none of us knew it was going to become so popular.

Barbara is a warm and wonderful character and I love playing her especially as it means I don't have to spend too long in make-up! she jokes. I do try and latch on to that reality in everything I play.

As for Grace, she may spend her life seeing and doing extraordinary and often disturbing things, but she is a woman who is at ease with herself, she is down-to-earth. If the BBC decided to make more Waking The Dead, I would love to have time to find out more about her.

We are all incredibly interested in what makes people abnormal, what makes them tick. It's just that Grace does it for a living.

Waking The Dead is on BBC1 on Monday and Tuesday.