Little Britain star David Walliams set off today on his most dangerous challenge so far - swimming the entire length of the Thames.

The comedian and panel show host is raising money for Sport Relief by swimming 140 miles over eight days from Gloucestershire to London.

Hundreds of wellwishers lined the river bank at Lechlade to give Walliams a loud send off and before taking the plunge into the icy river, he spoke to many of them.

The comedian said that when the swim got really tough, he would think about how the money he raised would help some of the poorest people in the world.

"I think about happy things, I think about what I'm going to eat when I get out," he said.