Little Britain star David Walliams is setting out on his swim to Africa today (Friday).

David, 36, and Olympic rower James Cracknell, 35, will swim 12 miles from Spain to Morocco. Their Sports Relief challenge across the Strait of Gibraltar is expected to take five hours.

David, who swam the Channel for charity in 2006, tested the water with his swimming partner in Tarifa, Spain, for an hour yesterday, in wetsuit, swimming cap and goggles.

In preparation for their 9am (GMT) start, last night the pair filled up on a carbohydrate-heavy meal of baked potato and chicken, washed down with tonic water.

The stretch of water they will swim across is a major shipping lane, meaning sharks will not be the only dangers they face.

Cracknell has already put in a marathon effort – he has rowed the Channel and cycled 1,395 miles to the starting point. The Olympic gold medallist has been nursing a painful blister on his buttock – which is expected to cause him even more trouble in the salt water – thanks to the six and a half days he spent in the saddle.

His wife, Beverley Turner, said: “I’m nervous about the swim because it’s a dangerous stretch of water… I will be watching from a support vessel with one eye trained on sharks’ fins and tankers.”

A spokeswoman said: “They are really excited about the swim.”

The charity effort can be supported at www.challengecracknell.com