The British comedian's aquatic challenge will see him swim 140 miles over the course of eight days, beginning the first week of September. Walliams will set off from Lechlade in Gloucestershire and finish at Big Ben in central London.

Swimming the Thames would prove a challenge for most confident swimmers, as the water is very cold and full of sewage. The Little Britain star commented: "Most people in the UK know the Thames, and most people think the idea of swimming in it is horrifying. And it is."

David is embarking on this gruelling mission in support of the Big Splash campaign; encouraging more people to go swimming.