Atwell wore a cobolt blue frock to the screening along with her smartly suited male co-stars, including a particularly dapper Ben Drew (aka Plan B).
Copyright: Rex Features
They were joined on the red carpet by director Nick Love, Jaime Winstone, in a black strappy dress, and sister Lois, in a floor-length black dress with frilled sleeves from Lily Allen's vintage label Lucy In Disguise.
Other celebrity guests included The Inbetweeners' Emily Atack, Claudia Winkleman, The Voice's Bo Bruce and Prince Harry's reported ex-girlfriend and model Florence Brudenell-Bruce.
Snatch actor Alan Ford, former As If actress Caroline Chikezie and Meg Matthews were also in attendance.