Simon Pegg

as Neil

Kate Beckinsale

as Catherine

Sanjeev Bhaskar

as Ray

Rob Riggle

as Grant

Robert Bathurst

as James Cleverill

Eddie Izzard

as Headmaster

Joanna Lumley

as Fenella

Marianne Oldham

as Rosie

Emma Pierson

as Miss Pringle

Meera Syal

as Fiona

Mojo

as Dennis the Dog

Robin Williams

as Dennis the Dog (voice)

John Cleese

as Chief Alien (voice)

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)

James David Robinson

as Steve

Judy Loe

as Canteen Lady

Alexa Davies

as Sandwich Girl

Ellie Green

as Lavender

Professor Brian Cox

as Self

James Kermack

as Policeman

Brenda Emmanus

as Reporter

Neville Phillips

as Author

Edward Fisher

as Mr. Eriksson

Simon Coleman

as Police Inspector

Ronan Summers

as Security Man

David Annen

as Newsreader

Mairi McHaffie

as Newsreader

Gavin Scott

as Newsreader

Richard Suchet

as Newsreader

Christopher Chesser

as Documentary Voice (voice)

Margarita Doyle

as Alien Computer Voice (voice) / Señorita Lopez

Jud Charlton

as Mortician

Lennon Clarke

as Bank Robber

John Bedford

as Ray Worshiper

Marli Bland

as Ray Worshiper

Basia Forrest

as Ray Worshiper

Liliana Gane

as Ray Worshiper

Lorna Lacey

as Ray Worshiper

Debbie J. Nash

as Ray Worshiper

Christian Palmer

as Ray Worshiper

Zara Sorensen

as Ray Worshiper

Chris Weeks

as Ray Worshiper

Robert Jones

as Pink Policeman

Chris Daniels

as Pink Policeman

Charlie Richards

as Pink Policeman

Samuel Timlett

as Baby

Lasco Atkins

as Party Guest (uncredited)

Hannah Blamires

as Photographer (uncredited)

Stuart Budd

as Passerby (uncredited)

Marat Khairoullin

as Zombie (uncredited)

Jorge Leon

as Celebrity (uncredited)

Tremayne Miller

as Book Launch Guest (uncredited)

Lockhart Ogilvie

as Ray Worshiper (uncredited)

Tony Pankhurst

as Father (uncredited)

Alan Yentob

as Man at Party (uncredited)