David Walliams has swum the English Channel and the length of the Thames, but his latest charity challenge should be a little easier – he is the new voice of the speaking clock.

The comic, who recently joined the judging panel on Britain’s Got Talent, has joined other stars including Kimberley Walsh and Gary Barlow in the bid to raise £1 million for Sport Relief.

David said he was “thrilled” to be taking part.

He said: “I was relieved to hear that BT only wanted my voice this time around and not for me to take on another gruelling challenge.”

David had to battle illness during his eight-day charity river swim last year and still undergoes physiotherapy after injuring a disc in his back during the ordeal.

He recently revealed how his supermodel wife put a halt to his plans to take on another physical challenge.

The Little Britain star, who married Lara Stone in 2010, said he wanted to fly to New York to meet his friend, adventurer Bear Grylls, to discuss a new endeavour.

The comic said: “It was only scaling a rock face, but Lara got really upset and said no…”

BT will donate 10p to Sport Relief every time someone uses one of its landlines to call the clock from today until April 9.

The clock has been providing the correct time since July 24 1936, and is accurate to five thousandths of a second.

Its regular voice is Sarah Mendes da Costa who became its fourth permanent voice after winning a competition in 2007.