Comedian David Walliams is close to raising £1million for Sport Relief, as he is expected today to complete his 140-mile swim of the Thames.

Despite suffering from 'Thames tummy' along the way – the river is home to a cocktail of bacteria – the Little Britain star is on course to finish around Westminster Bridge later today.

Sport Relief encourages the public to take part in sporting events to raise money for Comic Relief, which helps people in the UK and across the world's poorest countries.

David Walliams begins Thames charity swim

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Walliams began his epic journey last Monday at the river's source in Lechdale, Gloucestershire. Yesterday, he swam 21 miles – his longest day – to Teddington Lock.

The last leg of the swim this afternoon could be his toughest challenge yet, as he battles increased river traffic and a difficult current.

Thousands of cheering fans have turned out to support Walliams on the banks of the river along the way.

Walliams said: "I never expected this to catch the public's imagination like it has – there seems to have been a real carnival atmosphere around it which is lovely."