Boris Johnson today launched an extraordinary Twitter attack on the man who replaced him at City Hall with the hashtag 'uselessSadiq'.
The boss of the UK's diplomatic service used the undiplomatic language in a row over police station closures.
The Foreign Secretary is unhappy at plans to shut Uxbridge police station in his west London constituency.
London mayor Sadiq Khan claims government cuts leave him with no choice but to close half of London's police station front counters.
His Tory predecessor tweeted:
But a source close to Mr Khan accused Mr Johnson of being a 'stupid hypocrit', saying the former Mayor closed 63 police stations in 2013.