Robin Williams

Dennis the Dog (voice)

Eddie Izzard

Headmaster

John Cleese

Chief Alien (voice)

Eric Idle

Salubrious Gat (voice)

Simon Pegg

Neil

Rob Riggle

Grant

Sanjeev Bhaskar

Ray

Meera Syal

Fiona

Joanna Lumley

Fenella

Michael Palin

Kindly Alien (voice)

Mike Medavoy

Executive Producer

Terry Gilliam

Nasty Alien (voice)

Terry Jones

Scientist Alien (voice) / Van Driver

Kate Beckinsale

Catherine

Chris Chesser

Executive Producer

Robert Bathurst

James Cleverill

Alexa Davies

Sandwich Girl

Jason Garrett

Executive Producer

David Rogers

Executive Producer

Professor Brian Cox

Self

James Kermack

Policeman

Edward Simons

Executive Producer

Judy Loe

Canteen Lady

Marianne Oldham

Rosie

Emma Pierson

Miss Pringle

Mark Sandell

Executive Producer

Mojo

Dennis the Dog

James David Robinson

Steve

Ellie Green

Lavender

Brenda Emmanus

Reporter