Sick David Walliams may have to abandon his 140-mile Thames charity swim

Doctors are on standby on the riverbank after the comedian became "very poorly". He may have to abandon his 140-mile swim for charity Sport Relief.

A charity spokesman said: "David is not well at all and has had sickness and diarrhoea through the night.

"He is really hot and sweaty, so needless to say his pace has slowed today. He has taken on two days' worth of Thames water and it is reacting badly with his body. He does not want to eat because he is feeling so unwell, meaning he is struggling to get enough energy."

Walliams, 40, who has told of his fear of being attacked by swans, was this morning swimming past the village of Sutton Courtenay in Oxfordshire on the third day of the attempt. But his illness has meant he is struggling to swim at the pace he needs and he is already an hour behind.

Officials say the Little Britain star is being assessed by doctors every time he stops to ensure he is well enough to continue.

A Sport Relief spokeswoman said: "He is still ploughing on. He is swimming but he is not well. Every time he gets out he is assessed by the medical team. It is a vicious circle. He doesn't want to eat anything but he needs to eat to refuel."

The water of the Thames harbours a cocktail of bacteria such as e-coli, salmonella and hepatitis, as well as the 39 million cubic metres of raw sewage that finds its way into the river every year after heavy rainfall.

Walliams is said to be losing lots of salts and water as he swims, making it hard for his body to function as normal, so is being given sachets containing rehydration salts.

Walliams swam the Channel for Sport Relief in 2006, raising £1 million. He said the thought of helping relieve poverty in the UK and abroad would help keep him motivated as he swam through water with zero visibility.

Before he got in the water near the source of the Thames in Gloucestershire on Monday, he said: "I will think about pleasant things, nice songs and films.

"I suppose part of the struggle is mental, not just physical. I will think about the people, and that if I raise lots of money that will help."