What does a tickle look like? Mr Men turn 40

The Mr Men gang are turning 40.

The famous books were first conceived in 1971 when Adam Hargreaves - then just six years old - asked his dad Roger what a tickle looked like.

Since then, more than 100 million books have been sold. It is estimated that one is bought every 27 seconds.

Rick McShane from Waterstones in central London said the Mr Men books are often the first books children read.

"They are often the books children use in their first steps towards reading alone," he said.