Greg Dyke has ruled himself out of standing against Ken Livingstone in next year's election to be mayor of London.
Reports had linked the former BBC director-general with the post as a candidate with the joint backing of both the Conservative and Liberal Democrat parties.
But Mr Dyke today told Sky News that he was not interested in a joint candidacy, saying he would only have stood as an independent with the Conservatives and Liberal Democrats leaving the field open to him.
"I think it's too difficult for political parties to do that sort of thing," he said.
"I had a number of people ask me if I would be interested and… it was quite clear to me that it was not a runner."
Senior Liberal Democrats said the move may not have been possible in any case because it would contravene party rules.
But some reports cited Conservative leader David Cameron meeting with his Liberal Democrat counterpart Sir Menzies Campbell to consider the possibility of Mr Dyke running as a joint candidate.
Mr Dyke said he raised the idea after rejecting standing as the Conservative candidate before ruling out any decision to stand on the basis of his likely defeat.
"I'm not interested in spending a year of my life campaigning when I don't think I could win," he explained.
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