The BBC has hit back at viewers' attempts to rig the results of its Great Britons series.

The corporation says a "sophisticated method" has been used to multiple vote for Churchill, Darwin and Shakespeare, three of the 10contenders in the running to find the nation's greatest.

A spokesman said the BBC team monitoring the votes was "onto the culprits".

"Our team are constantly monitoring the votes to make sure nothing untoward is happening," she said.

"We did identify that people had been attempting to rig the voting but those votes have now been eliminated."

Tactical voting

The series, which has attracted viewing figures of three million and sparked debate on 200 internet news groups, has also inspired some tactical voting from Brunel University students.

They have begun a campaign to make Isambard Kingdom Brunel - their university namesake - the winner.

The BBC has been inundated with votes on its website and phone lines for the Bristol-based engineer - a move which has seen him surge into the lead.

A BBC spokesman said the campaign was "entirely legitimate".

Clarkson is championing Kingdom Brunel

"We are not overly worried about this and we hope it encourages others to do the same," she said.

"It is fantastic to see that people are prepared to go to these lengths because they are so passionate about the series."

Brunel, probably best remembered for the network of tunnels, bridges and viaducts he built for the wide-gauge Great Western Railway, is also being backed by BBC presenter Jeremy Clarkson.

He has been reinforcing his case for Brunel through his columns in the Sunday Times.

The push for Brunel has seen Diana, Princess of Wales fall into second place.

Following closely behind are Sir Winston Churchill, with 16% of the votes and Darwin, with 11%.