Barton played Marissa Cooper in The OC

The 21-year-old, who starred in US teen drama The OC, will be playing the character JJ French.

Cameras are already rolling on the new version of the 1950s comedies, which stars Rupert Everett in the dual role of the headmistress and her brother.

The Ealing Studios project has also attracted celebrities like comedian Russell Brand and model Lily Cole.

Classic movies

Bridget Jones's Diary actor Colin Firth stars as an MP who has plans to turn St Trinian's into a respectable institution.

Scenes have already been filmed in Trafalgar Square and in various other locations around London.

Ealing Studios produced some of Britain's best-loved comedies of the 1940s and 1950s, including Whisky Galore and The Ladykillers.

The first St Trinian's film - the Belles of St Trinian's - was made in 1954 and starred Alastair Sim as the headmistress, alongside Joyce Grenfell and George Cole.