Simon Pegg

Neil

Kate Beckinsale

Catherine

Sanjeev Bhaskar

Ray

Rob Riggle

Grant

Robert Bathurst

James Cleverill

Suzy Eddie Izzard

Headmaster

Joanna Lumley

Fenella

Marianne Oldham

Rosie

Emma Pierson

Miss Pringle

Meera Syal

Fiona

Mojo

Dennis the Dog

Robin Williams

Dennis the Dog (voice)

John Cleese

Chief Alien (voice)

Terry Gilliam

Nasty Alien (voice)

Eric Idle

Salubrious Gat (voice)

Terry Jones

Scientist Alien (voice) / Van Driver

Michael Palin

Kindly Alien (voice)

James David Robinson

Steve

Judy Loe

Canteen Lady

Alexa Davies

Sandwich Girl

Ellie Green

Lavender

Brian Cox

Self

James Kermack

Policeman

Brenda Emmanus

Reporter

Neville Phillips

Author

Edward Fisher

Mr. Eriksson

Simon Coleman

Police Inspector

Ronan Summers

Security Man

David Annen

Newsreader

Mairi McHaffie

Newsreader

Gavin Scott

Newsreader

Richard Suchet

Newsreader

Christopher Chesser

Documentary Voice (voice)

Margarita Doyle

Alien Computer Voice (voice) / Señorita Lopez

Jud Charlton

Mortician

Lennon Clarke

Bank Robber

John Bedford

Ray Worshiper

Marli Bland

Ray Worshiper

Basia Forrest

Ray Worshiper

Liliana Gane

Ray Worshiper

Jorge Leon

Celebrity (uncredited)

Alan Yentob

Man at Party (uncredited)