Finn Cole as Don Wallace

Asa Butterfield as Willoughby Blake

Hermione Corfield as Clemsie Lawrence

Simon Pegg as Meredith Houseman

Michael Sheen as The Bat

Nick Frost as Woody Chapman

Tom Rhys Harries as Clegg

Isabella Laughland as Kay

Kit Connor as Wootton

Jamie Blackley as Caspar de Brunose

Margot Robbie as Audrey

Jo Hartley as Babs Wallace

Jane Stanness as Matron

Louis Strong as Smudger

Jassa Ahluwalia as Yuri

Cory Chambers as Bello

Alan Drake as Butler

Charles Evans as Mikey

Charlie Fitzherbert as Tomkinson

Alhaji Fofana as Chibwe

Hanako Footman as Poppet

Gary Golding as Hedger

Rohan Gotobed as Scholar Bartlett

Nick Kellington as The Beast

Alex MacQueen as Lambert

Levi Masoet as Dr. François

Neil Pendleton as Red Dreads

Max Raphael as Hargreaves

James Woodroffe as Teddy Chapman

Joshua Squire as Olympus Boy (uncredited)

Toby Cordes as Sparta Boy (uncredited)

Ted Day as Sparta Boy (uncredited)

Thomas Farrow-Tomson as Sparta Boy (uncredited)

Harry Isherwood as Sparta Boy (uncredited)

Aron Jackson as Sparta Boy (uncredited)

Mateusz Kobylec as Sparta Boy (uncredited)

Sam Redland as Sparta Boy (uncredited)

Zaak Conway as Tiny New Boy (uncredited)

Jack Webb as Xenephon Boy (uncredited)

Ben Wheeler as Xenephon Boy (uncredited)

Lee Charles as Special Security (uncredited)