American singer Joan Jett remembers the moment she realised Hollywood's hottest young female star was the perfect person to play her part in the rock bio-pic The Runaways.
It was all down to the haircut. Kristen Stewart , heroine of the hugely successful Twilight series, agreed to chop her flowing locks into the short, shaggy style made famous by Jett.
'I was curious about Kristen's commitment, so I asked if she'd be cutting her hair,' says Joan. 'She was still filming Eclipse, the third Twilight movie, so I'd have understood if she wanted to keep her hair long.
'But she was unequivocal. The hair came off, and she got into my character. The way she moved and talked was just like me.'
Nailed it: Joan Jett, left, has been full of praise for Kristen Stewart, right, after she portrayed The Runaways singer
'I spent hours telling her the intimate details about the Runaways,' she continues.
'I dumped everything on her. I gave her live tapes from 1976 and tapes of me speaking when I was 14 to help with the accent. I wanted her to understand me as a musician, but I wanted her to get me as a person, too. And she nailed it. When my family saw the movie, they thought it was footage of me!'
Joan Jett is the real deal. Now 51, she holds the anti-corporate ideals of the Seventies dear, but is shrewd enough to run her own record label. As executive producer, she oversaw the making of The Runaways film.
Sitting in a London hotel, dressed in black and with that shaggy haircut intact, she is every inch the tough rocker. Despite her teenage years in California, Jett's accent retains an East Coast twang.
The only comparable figure is Chrissie Hynde, and even Hynde' s first hits with The Pretenders came four years after Jett started The Runaways.
'I'm a tomboy, and I've always felt tough,' she says.
'But I'm also vulnerable. The leather jackets and heavy eye make-up were my teenage armoury. They gave me protection.'
Jett, an accomplished guitarist, formed The Runaways with singer Cherie Currie, drummer Sandy West, bassist Jackie Fox and lead guitarist Lita Ford in 1975. Despite co-writing many of their own songs, the band were mocked by the American rock establishment.
'I didn't want a big fight, so we played one, last gig on New Year's Eve in 1978, and ended it there.'
They toured with Van Halen and Tom Petty, but commercial success came mostly overseas, particularly in Europe and Japan. 'I thought music was a liberal world, but a lot of people thought girls couldn't play rock 'n' roll. As a guitarist, I didn't try anything fancy. I played along with Sandy's drums. I was a fan of records with big riffs, like David Bowie's Rebel Rebel.'
The career of The Runaways spanned two eras - glam rock and punk. Jett recalls a UK visit in 1976 when she 'arrived as a glam rocker and went home a punk'.
But, by 1978, it was all over.
'It was a slow disillusion,' says Joan.
'There was tension, but that wasn't what broke us up. Cherie had left 18 months previously to make mellower music. Sandy and Lita wanted to move towards heavy rock. I was happier doing straight- up rock 'n' roll. I didn't want a big fight, so we played one, last gig on New Year's Eve in 1978, and ended it there.'
Unable to secure a deal, she released her first solo album, Bad Reputation, independently in 1980. Then, a year later, with new band The Blackhearts in tow, she hit pay- dirt after covering an obscure track by Seventies power-pop trio The Arrows.
'After The Runaways broke up, all the girls were offered solo deals apart from me,' she says. 'The record labels found my image too frightening.
'But that changed after I did I Love Rock 'N' Roll, which connected with millions of fans. That song vindicated me for following my instincts.'
Old school: Picture shows the 1970's female rock group 'The Runaways' from left, Joan Jett, Sandy West, Cherie Currie, Vicki Blue and Lita Ford
They probably will, although the film, which features Joan and Cherie sharing a kiss, will fuel speculation about Jett' s sexuality.
'People have been asking me those questions since I was 16,' says Joan.
'They want to be spoon fed.
'They should listen to the lyrics - I've always sung to everybody, and I want both boys and girls to think I'm singing to them. The filmmakers wanted to play up the salacious side, but I didn't want to tell too many crazy stories.
'I'd like The Runaways to be remembered for other things - the tours we did, the bands we played with and the people we inspired.'
Joan Jett And The Blackhearts Greatest Hits is out now. The Runaways opens on September 10.
