Almost 180,000 people have voted in a poll to find the greatest Briton of all time in less than four days.

Engineer Isambard Kingdom Brunel has taken an early lead with 35% of the vote after he was the first of the BBC's top 10 Great Britons to be featured in the series.

Standings on 23 October

1. Brunel 2. Churchill 3. Darwin 4. Princess Diana 5. Shakespeare

Motoring presenter Jeremy Clarkson set out a powerful argument for Brunel's achievements in a show in Tuesday that was watched by 3.5 million people.

But Sir Winston Churchill is still the bookmakers' odds-on favourite to win.

The Great Britons project has seen 100 of the most influential figures from past and present whittled down to 10, with viewers invited to vote for their favourite.

Churchill is now second in the public poll, which opened on Sunday.

The BBC's Andrew Marr is to argue for Charles Darwin

Charles Darwin, the father of the theory of evolution, is currently third, with Diana, Princess of Wales, fourth and William Shakespeare fifth.

Brunel, the 19th Century engineer and railway pioneer who designed Bristol's Clifton suspension bridge, jumped from fifth to first after Clarkson's BBC Two profile.

Its viewing figures were seen as a success for a factual programme, attracting just 500,000 fewer viewers than BBC One's prime-time talent show Fame Academy.

Series producer Mark Harrison said: "It is wonderful that such a profound issue as the attempt to define greatness has become a national obsession.

"It shows that top quality documentary can spark enormous debate and passion - as well as participation."

The next profile will be of Darwin, presented by the BBC's political editor Andrew Marr.

Bookmakers' odds

Churchill - 4/9 Princess Diana - 4/1 Shakespeare - 7/1 Darwin - 8/1 Brunel - 20/1 Source: Ladbrokes

The top 10 also includes Sir Isaac Newton, Queen Elizabeth I, John Lennon, Oliver Cromwell and Nelson.

Anne Robinson, who is presenting some of the shows, said she was "dumbfounded" that Princess Diana made it to the top 10.

The original 100 also included surprises such as music stars John Lydon and Boy George.

People can vote for the winner by telephone, internet or on interactive television.