Mr Livingstone's political opponents have told BBC London political editor Tim Donovan the tour raised questions about judgement and was "humiliating and embarrassing".

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Tim O'Donovan, an 81-year-old retired insurance broker from Windsor, used the court circular - introduced by King George III and published daily in the Times, the Daily Telegraph and the Scotsman - to come to his estimate.

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And I also want to acknowledge Bob Ryan, who worked with Shaun Donovan extensively on this issue, as well as Tim Massad of Treasury.

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