Nick Clegg has called Boris Johnson a "conventional" politician who "treats his political ambition a bit like he treats his hair."
Clegg said the Mayor of London, who announced his intention to stand at the next General Election, liked to pretend he did not care about his appearance or career - but was actually "fixated" with them.
"The thing about Boris Johnson is despite all the kind of clumsiness and bumbliness, he's actually a really, really ambitious politician," the Deputy Prime Minister said on his regular LBC radio phone in.
"He wants everyone to think that he doesn't really care, but he actually really, really does care."
More top news
The live stage version of Peter Kay's Phoenix Nights has reportedly been cancelled after actor Ted Robbins collapsed on opening night.
The much-loved local character, who had lived on the city's streets for decades, died in hospital this week after falling ill.
Man City remain five points behind Chelsea in the Premier League title race after a 1-1 draw at Stamford Bridge