He has ridden out many much more serious storms over the past three years, but suddenly a meeting with the Mayor of London produces the resignation of Sir Ian Blair. The Metropolitan Police Commissioner has had his share of critics, but his resilience in the face of the most hostile treatment has been consistent. So, what happened? Why now? And what are the consequences of this political power struggle for control of our largest police force?

The stories circulating since last Thursday have varied widely. Some suggest that this was just another example of Boris the loose-cannon Mayor acting without the knowledge of the Metropolitan Police Authority, the Home Secretary or the Conservative Party hierarchy. Others say it was the successful culmination of a long-standing Tory plot to oust Blair and bring in someone less sympathetic to New Labour.

I've never been much of a fan of conspiracy theories, and anyway there is more than a sniff of cock-up about this series of events. The fact that the normally garrulous Boris Johnson was refusing to answer questions in the immediate aftermath of Blair's resignation seemed a bit fishy. Perhaps it was just a momentary pause while the Tory plotters got their stories straight? More likely, it seems to me, is that Blair's resignation came as a shock to the Tory hierarchy and that Boris had some explaining to do.

David Cameron has been assiduous in his attempts to rein in his maverick mayor. However, Boris has form. He's a serial offender and that he was acting on his own initiative seems much more likely than some grand scheme hatched at Tory Central. Indeed, there's a further possibility. Perhaps the Mayor's initial refusal to answer questions was because he was in shock too. Johnson was in the process of taking over as chair of the MPA and had a private meeting with the Commissioner. His views of Blair are well known and he undoubtedly made it clear again that he would do whatever was within his power to ensure that Blair didn't see his contract through to 2010. I imagine he did this little expecting that a man who has described himself as "a bit of a limpet" would decide that now was the time to go.

This is all speculation. But, if true, it would give the lie to the assumption that Ian Blair can't do politics very well. This is a man who was widely respected, but was equally widely expected to lose his job at some stage. Perhaps in the end he managed to maintain some control over his departure. In doing so he wrong-footed critics and is leaving with many observers bemoaning his treatment and highlighting the many positive aspects of his commissionership. Any stink at the moment surrounds Boris not Blair.

The shenanigans of the past few days make one thing abundantly clear. We need to sort out the relationship between politics and policing. First, to all those who say that politics has no role in policing – forget it. Politics has always been part and parcel of policing, long before Boris. The big issue for us is how should a police service, and its senior officials, be made democratically accountable? Who should govern them and how?

In most cases, in my view, they should be directly answerable to locally elected police authorities. Such bodies exist, though they are neither entirely elected nor sufficiently powerful. For too long the Home Office has been the dominant partner. The case of the Metropolitan Police is a little different, however. The Met has a series of national responsibilities, not least counter-terrorism, and these mean that the Home Secretary necessarily plays an important role in overseeing what it does and in appointing the Commissioner, in consultation with the police authority.

But, you say, surely my plea for a greater role for local control of policing will lead to the proliferation of Mayor Johnsons all over the country? It needn't. We can reform and reinvigorate police authorities without institutionalising the shambles of the last few days. We must resist the calls for the creation of some form of American-style mayoral control over policing for such a model threatens many of the better aspects of the British system. Too much mayoral power is a recipe for nasty populist politics and short-term fixes rather than considered local democratic oversight.

The commissionership of the Met is too large, too complex and too important a job to be in the gift of the Mayor. This is a problem of New Labour's creation and one it must urgently fix. Home Secretary Jacqui Smith and her colleagues need to get a grip of this before more lasting damage is done. The dangers are well illustrated by some of the ideas being spread by the Mayor's aides over the past few days. First they suggested it would be reasonable to wait until there was a Conservative home secretary before appointing a permanent replacement for Sir Ian. This would mean a temporary commissioner for 18 months followed by what would be seen as a nakedly political appointment. Fragile public faith in policing would be tested to the limit. The Met would surely not stand for it either.

Finally, what of the recent suggestion that the Johnson team's favoured candidate to replace Blair is the Los Angeles police chief, Bill Bratton? Highly experienced, charismatic and coming with the reputation of having championed New York's experiment with so-called zero tolerance policing, one can see why Bratton's name gets mentioned. But he has no experience of British policing and little knowledge of our capital city and what makes it tick. He might just convince Boris, but it is hard to see him convincing the Home Secretary, the MPA, the officers of the Met, or the people of London. And if Boris mentions the idea again, it is worth reminding him that Bratton only survived for two years in New York before being sacked. Yes, by the Mayor.

Tim Newburn is professor of criminology at the London School of Economics ( t.newburn@lse.ac.uk)