Walliams' writing tips: 'Make baddies funny'

Ever wanted a famous author to surprise your school assembly and give you writing tips?

Well, that's what happened to pupils at a London school when David Walliams turned up one morning.

The author and Britain's Got Talent judge surprised a hall of 200 children and gave some top tips for becoming a writer.

He also read extracts from his books, including Gangsta Granny and Windy Mindy from The World's Worst Children - the follow-up has just been released.

Watch the clip to see more.