GIRLS Aloud singer Sarah Harding admits she is still learning the art of acting as she stars in her third film, St Trinian’s: The Legend of Fritton’s Gold.

“It’s a work in progress,” says Sarah, who appeared in the first St Trinian’s film in 2007 and the thriller Bad Day.

“I was trained to act in the past, but no one really knew that – so it’s a case of getting that out there. I just want to build it up gradually because there’s always a lot of speculation when you do that transition from singing to acting.

“You almost feel like you have more to prove. So I’m going to do it properly. I have an acting coach I work with and if I’m lucky enough to get another part, then I’ll take that script with me to her and I’ll start working and researching the character. I’m not taking it lightly.”

In the St Trinian’s sequel, 28-year-old Sarah plays rebellious schoolgirl Roxy. “She’s probably a more laid-back version of myself,” she says. “She’s too cool for school and she’s not a team player to start with – she doesn’t feel like she needs anyone and doesn’t really feel like she’s going to be hanging around for long.

“But then she gets involved with some of the things that are going on and starts getting more excitable and losing her cool slightly. So it’s a nice journey and relationship you see develop between her and the girls.”

Sarah is starring alongside Rupert Everett as Miss Fritton, Colin Firth as Geoffrey Thwaites and David Tennant as Lord Pomfrey. “David plays the baddie so he’s my enemy! He’s in a few scenes with us, yes and he’s great. I didn’t actually realise he is Scottish,” she says.

“When I first met him I was like ‘Bloody hell! You’re a Scot’. I’d always assumed he was English because of his well-spoken accent on Doctor Who. I’d never spoken to him before. But he’s a lovely fella. Colin Firth is a sweetheart; Rupert is very, very funny – very dry.”

Looking to her future acting opportunities, Sarah is reading a script at the moment.

“I’ve had a couple of others and you know what, I think when a part is right I’ll know and then I’ll go for it and I’ll screen test and I’m not going to rush into it. I’d rather wait and get it right,” she says.

Media talk linking her with a part in The Brazilian Job, a follow-up to The Italian Job, is wide of the mark.

“I’ve never even heard of that. I don’t know what they’re talking about,” she says. “I don’t read too much any more, I just look at the pictures and go ‘Is that a good picture?’. Okay, that’s fine. I’d rather not get too wrapped up in all that stuff. You just have to laugh it off.”