Nick Clegg's job in government is to serve as David Cameron's condom, Boris Johnson has suggested.
Speaking during his monthly LBC radio show on Tuesday morning, the mayor of London said the deputy prime minister was "a lapdog who has been skinned and turned into a shield" to protect the prime minister.
Boris added that Clegg was "there to perform a very important ceremonial function" as a "prophylactic protection device for all the difficult things David Cameron has to do".
The mayor and Lib Dem leader have a long running, if usually light-hearted, feud. Clegg likes to refer to the mayor as "slacker Johnson" for being lazy. And in a more serious attack, the deputy prime minister also said Boris was guilty of "unpleasant, careless elitism". For his part, Boris recently described Clegg as a "great yellow albatross".
But Boris insisted today that he did not "want to get in to some sort of endless ding-dong with poor old Cleggers".
The mayor had been asked whether he agreed with Clegg that George Osborne's plans to cut a further £25bn from public spending was "extreme".
Boris said there was "more to be done in getting the deficit under control" and indicated he agreed with many Conservative MPs who think international development aid should be cut.
"They should be looking at all areas of public spending," he said. "I am still slightly perplexed about why we contribute aid money to some of these countries that are on the path to prosperity."
Cameron has pledged he will not abandon his pre-election promise to keep spending 0.7% GDP on development aid.