Doctor Who star David Tennant is to line up with a glamorous new foe - Girls Aloud singer Sarah Harding. The pair are to star in film comedy St Trinian's 2: The Legend of Fritton's Gold. Filming for the sequel to St Trinian's, which made £12million at the UK box office, started yesterday with earlier stars Rupert Everett and Colin Firth. An insider said: "It is quite a coup to land Sarah and David. Sarah had a little part in the last film along with the rest of the band as they sang the final song. "She enjoyed it so much it has been expanded and now she's a major part of the cast. "And to get David for his first film after Doctor Who is just fantastic." Harding, 29, joins the girls of St Trinian's as cool new pupil Roxy hunting for headmistress Miss Fritton's legendary family fortune. Tennant stars as villain Pomfrey who heads secret women-hating society AD1. The Mirror.