Simon Pegg as Neil Clarke

Kate Beckinsale as Catherine

Robin Williams as Dennis the Dog (voice)

Rob Riggle as Grant

Sanjeev Bhaskar as Ray

Joanna Lumley as Fenella

Marianne Oldham as Rosie

Eddie Izzard as Headmaster

Robert Bathurst as James Cleverill

John Cleese as Chief Alien (voice)

Judy Loe as Canteen Lady

Brian Cox as Self

Meera Syal as Fiona

Emma Pierson as Miss Pringle

David Annen as Newsreader

Mairi McHaffie as Newsreader

Gavin Scott as Newsreader

Terry Gilliam as Nasty Alien (voice)

Eric Idle as Salubrious Gat (voice)

Terry Jones as Scientist Alien (voice) / Van Driver

Michael Palin as Kindly Alien (voice)

Alexa Davies as Sandwich Girl

Neville Phillips as Author

Ronan Summers as Security Man

Jud Charlton as Mortician

James Kermack as Policeman