Ken Livingstone went on to win the election earlier this month

Radio Authority chairman Richard Hooper said the incidents were a "flagrant breach" of the rules on political impartiality which govern broadcasters.

Evans' outburst, on 21 March, came just 11 days after the authority reminded all stations of its rules on impartiality, specifically because of the forthcoming election.

The broadcaster declared his support for Mr Livingstone on his show after Labour's candidate Frank Dobson made a disparaging remark about red-haired people.

Frank Dobson's remarks about redheads angered Evans

He initially made his views public after the 0800 news bulletin and repeated them an hour later, saying he had donated money to the Brent East MP's campaign.

The fine is the fifth since Virgin began broadcasting in 1993. Evans' Ginger Media company - now part of the Scottish Media Group - bought the station in 1997.

The Radio Authority - which regulates UK commercial stations - said: "The station had not only failed to ensure that its presenters were fully aware of the rules on due impartiality but had allowed a second breach to be aired."

This was a flagrant breach of the rules surrounding political impartiality - we are determined it shall not be repeated

Radio Authority chairman Richard Hooper

The fine would have been higher if the station had not taken the steps it did to "make amends" for the breach the following day, the authority added.

Mr Hooper said: "Political impartiality is a cornerstone of British broadcasting, strongly supported by all governments and public opinion over many years.

"This broadcast by Virgin was a flagrant breach of the long-standing rules surrounding political impartiality, made worse by the fact that the broadcast took place in the run-up to that most sensitive of political events, an election.

This is the fifth fine for Virgin Radio, which Evans bought in 1997

"The breach also demonstrated a critical failure of compliance by the licensee and we are determined that this shall not be repeated."

Virgin accepted the ruling, issuing a statement saying the comments were "in response to criticism of Chris Evans by another mayoral candidate which were reported in that morning's newspapers".

The station's chief executive, John Pearson, said: "Chris Evans is a superb broadcaster, who was drawn into making comments during an extended election campaign.

"For this, we have apologised to the Radio Authority."

Evans pledged �100,000 to Mr Livingstone's campaign in a newspaper interview, which prompted Frank Dobson to say: "My old mum told me to steer clear of redheads."

In response, Evans upped his donation to �200,000.

Last year the authority fined London rock station Xfm and Sheffield pop station Hallam FM �50,000 each for comments made on air by DJs in separate incidents.