Boris is a Mayor who likes to be liked, and it was when his questioners probed for admissions of failure, arrogance or regret that you could see and hear them get under his skin. The press conference just ended at City Hall is one of the bare handful he's submitted himself to in his place of work, preferring themed location settings where he can more easily joke, duck and dive. It started smoothly enough, but the hard pressure started taking its toll when the London specialists in the room at long last had a chance to pin him down for longer than the length of a cheery soundbite.

There was, then, no sign of the usual cakes and ale. He was on the back foot, and he could be there for quite a while. People wanted to know what Boris had actually been doing all this time. What assurances had he and his deputy Kit Malthouse extracted from John Yates, the officer who's just resigned over the hacking affair, that he was exploring the hacking allegations seriously as they increased in gravity and number? As a hacking victim himself, what assurances had he obtained from Yates, when chairing the Metropolitan Police Authority, that he had looked very carefully at the number of other people who might have been hacked? Had he been "asleep on this one?"

Boris stuck to his familiar line, that he'd simply taken on trust what he'd been told. He replied that Yates had been "very clear to me" that there had been "nothing new" coming up. Malthouse backed him up. Clearly, if someone else had made mistakes it wasn't their fault. But then Boris was asked if he, like Sir Paul Stephenson, should take responsibility for his failures and resign. Did he regret calling phone hacking allegations "codswallop"? Wasn't his judgement in question here? Did he regret recently praising Rupert Murdoch for his "very considerable contribution" to journalism? Would he apologise for having mocked the people who, unlike him, had stuck at the hacking story? How about for not bothering to make sure Yates took a good, long look at those 11,000 pages of evidence on his watch?

The gathering insinuation was that Boris had just been playing at being responsible for policing; playing, maybe, at being Mayor. It's the charge his political enemies long to stick to him. The more he offered the excuse that it wasn't his fault, guv, the less his audience was satisfied. You could sense the temperature rise. Then Jon Snow from Channel 4 News took him through the long history of Met-News International links and personnel crossovers, going right back to John Stevens's time. Surely it had been clear for years that something wasn't right?" And that's why we're having this investigation!" was the Mayor's angry bark of a reply. Patience snapped. Bonhomie gone. Boris, behind the mask.