Theo Stevenson
Horrid Henry
Anjelica Huston
Miss Battleaxe
Ross Marron
Perfect Peter
Parminder Nagra
Miss Lovely
Mathew Horne
Dad
Siobhan Hayes
Mum
Richard E. Grant
Vic Van Wrinkle
Prunella Scales
Great Aunt Greta
Scarlett Stitt
Moody Margaret
Lloyd Howells
Rude Ralph
David Schneider
Soggy Sid
Kimberley Walsh
Prissy Polly
Billy Kennedy
Weeping William
Noel Fielding
Ed Banger
Jo Brand
Demon Dinner Lady
Helen Lederer
Rich Aunt Ruby
Rebecca Front
Miss Oddbod
Jack Sanders
Aerobic Al
Reuben Lee
Brainy Brian
Helena Barlow
Sour Susan
Nikita Mistry
Gorgeous Gurinda
Frank Kauer
Spotless Sam
Joshua-James Thomas
Goody Goody Gordon
Tyger Drew-Honey
Stuck-Up Steve
Tamsin Heatley
Madam Tutu / Fang (voice)
Dominic Wood
2C4S Presenter 1
Richard McCourt
2C4S Presenter 2
Zac Gabriel Werb
Tidy Ted
Keely Cat Wells
Alice
Kia Pegg
Vicious Vicky
Sam Davis
Keepy Uppy Boy
Freddie Rose
Schoolboy (uncredited)
Harvey Walsh
Schoolboy (uncredited)