A MAN attempting to be the first person to swim the River Thames has gone ashore and walked to Downing Street to lobby the Prime Minister on climate change.

Lewis Pugh, 36, is on the eighteenth day of his epic swim which has seen him cover 222km and spend 85 hours in the river.

Mr Pugh had planned to complete the swim in 15 days, but the drought and the record-breaking heat has slowed him down and he now plans to finish the 325km swim on Sunday afternoon at Southend-on-Sea, in Essex.

"It's been a tough swim. The lack of water has really slowed me down and I have not been able to keep to a steady pace whilst regularly having to jump out of the river to walk around the closed weirs," he said.

"That is why I am stopping off at Downing Street, to ask Tony Blair to urgently put climate change at the very top of his agenda, by putting policies in place to ensure that we meet our national climate change targets to reduce CO2 emissions."

The swim, which started just south of Cirencester in the Cotswold Hills, has so far taken him through Oxford, Reading, Henley-on-Thames and Windsor.

The heat as forced him to constantly stop to apply sunscreen and recently he was hospitalised due to exhaustion. But reaching the capital will provide some relief for the marathon swimmer, as the River Thames becomes tidal after Teddington, west of London.

"Frankly I can't wait to get onto a piece of river that has some flow to it. The last two weeks have been an unbelievably hard grind, both on my physique and also mentally," Mr Pugh said in his online diary.

"I am excited to be faced with some quick swimming and also the fact that I am entering the really historic part of the Thames."

In 2003 he completed the first swim in the Barents Sea by swimming around North Cape, Europe's most northern point.

The following year, he swam the entire length of Norway's longest fjord. In August 2005 he plunged into the Arctic Ocean near the North Pole and swam 1km to break the world record for the most northern long distance swim.

Earlier this year he became the first person to complete a long distance swim in all five oceans of the world, when he completed a long distance swim in the Indian and Pacific Oceans.