Julie Walters has made a name for herself playing a string of bolshy, straight-talking women. With a touch of steel and handfuls of humour, she's taken on determined student Rita in Willy Russell's Educating Rita, pushy-yet-supportive ballet teacher Mrs Wilkinson in Billy Elliot and censorship champion Mary Whitehouse in Filth: The Mary Whitehouse Story. She's even stripped off, alongside Helen Mirren and Celia Imrie, for Calendar Girls.
But nothing prepared her for one-off drama Mo, in which she plays Mo Mowlam, the British Labour politician and Secretary of State who fought for peace in Northern Ireland.
In fact, bringing to life one of the most colourful characters in recent political history was so daunting she nearly ended up turning down the role.
The 59-year-old explains: "When I got the script I thought, 'Fabulous, this is such a good script, I'll do it.' Then I got all the research stuff on her and I thought, 'God, I'm nothing like this woman at all, and she's got this strange voice. How am I ever going to embody that?'
"Then, I rang my agent and said, 'I'm not sure I should do this. I cannot be anything like her.' He said, 'Julie, I've never said this to you before but I'm going to say it to you now: that is a load of bollocks. Get the wig and the glasses and you'll be fine.'"
Mowlam's wig became one of the MP's trademarks towards the end of her life as she battled with a brain tumour. She even famously took it off during a tense discussion leading to the signing of the 1998 Good Friday Agreement, apparently to lighten the atmosphere.
The politician's voice was also something that Walters had to master, and her own voice suffered as a result. She said: "I couldn't remember how she spoke, and Grant [Walters' husband] said, 'Well, it's kind of squeaky.' I said, 'Don't be silly. Mo?' And they got all these videos of her together for me, and there she was with this voice. And I thought, 'Bloody hell. I'll ruin my voice doing it.' It's better now, but for months a whole piece of my vocal chords closed down because I didn't warm up like I would have if I had been singing."
Walters was also frightened to play a personality who was so well-loved. It is unusual for a politician to have such a good public profile but, after retiring from parliament, Mowlam was a regular on TV talk shows -- including the saucy ones such as The Graham Norton Show -- and even had an advice column in lads' mag Zoo.
"People thought they were getting straight talk from her, and she cared about ordinary folk. She genuinely did, and they knew that. And they're so used to politicians out for their careers, so she just stuck out. And she was so uninhibited, partly because of the tumour, but it was all part of her.
"They reckon that she had that tumour for 30 years and then suddenly it went out of control. She was very, very straight and she was very bright, so she could argue and cut through the c**p," Walters says.
Central to everything is Mowlam's strong relationship with her husband Jon.
Walters coos: "They were very much in love. They were shagging all the time! Her 'non-w**ker-banker' husband, she used to call him. David Haig is absolutely wonderful in the role."
It is the focus on this relationship and on Mowlam as a three-dimensional person which makes the drama accessible for all viewers, Walters says.
"It's not just for those interested in politics. It's a very human story, this film. The politics is interesting, but it's almost in the background, eclipsed by Mo. Which everything was. She was this tornado that went through life with everything else happening around her.
"It's about who she was, it's about her love for her husband, it's about caring for people, it's about dealing with the tumour, it's about her courage. But it's not sentimental, that's why it's special."
Mo explores the politician's life until its end in 2005, when she died aged 55. Strangely for Walters, her last big television role was playing Anne Turner, a woman with an incurable degenerative disease who fought for the right to die, in A Short Stay In Switzerland.
She jokes: "It did occur to me that I'd just played someone dying . . . but I thought, 'This is a good script. I can't turn it down just because it has me dying again.'"
These last two roles are a sharp contrast to Walters' work with Victoria Wood. She delighted viewers with her portrayal of dowdy cleaner Mrs Overall in Wood's mock soap opera Acorn Antiques and is a regular in Wood's sketch shows.
She counts Mrs Overall among one of the favourite characters she has played, as well as her role in Educating Rita, which was filmed in Dublin. The actress also thinks it was working with Wood and starring in Educating Rita that helped her break into the industry.
"I'd just started to be known through Victoria's stuff with Wood And Walters, which came out very close to Educating Rita. It was quite a grand slam in a way for me, really useful for me doing those two things. And at the same time . . . I did a play with Alan Bennett in it on television, and also Boys From The Black Stuff. It all came out in a short space of time."
It was a dream come true for Walters, who wanted to be an actress from a young age: "I was sort of shy and under-confident, but I also had that thing of being the class clown and the person who impersonated people in the family and at school."
The breakthrough was encouraging for Walters' mother who was worried about her going into acting. "She said: 'She'll be in the gutter before she's 20!' She was very scared, she thought there was no pension."
Little did she know that her daughter would still be reeling in the big roles aged 59, and that -- yes -- she does have a pension.
Mo will be shown on Channel 4, on Sunday, January 31