The next couple of days will dictate whether a crisis becomes a disaster, or another crisis managed to a relatively successful conclusion.

Any crisis requires strong clear leadership, and when it is a crisis on this scale, with people fearing the loss of control of the streets, that has to come from the Prime Minister. That means clear and hard-headed analysis, finding the right words to sum up the situation, and the right actions required to bring the situation under control. I genuinely wish him well as he seeks to do those things today.

Boris Johnson’s leadership is also going to be tested, and how be handles that test is likely to decide the outcome of the next London mayoral elections.

As I saw when he and I launched a charity bike ride recently, Boris has a certain natural appeal. Most of the Cabinet would have to fall off a bike before anyone was interested, and even then most passers by would struggle to recognise them. Boris just has to mount a bike and wave to get people waving back from the top decks. In era of Cabinet blandism, his blondism goes a long way, which is why most of the Cabinet resent him.

But he has never really had a crisis of this sort to deal with, and the amiable overdone buffoonery will not cut it as an approach to current events. He has to show he can do serious leadership as well as the celebrity stuff for which, frankly, he is better known.

Ken Livingstone got a bit of flak last night for seeking to link the riots to spending cuts, but the interviews I heard were fair and reasonable, rightly condemnatory of criminality, but rightly also insisting there has to be a debate about the sense of hopelessness many young people feel.

He was right too to point out that Boris Johnson’s main contribution to political debate recently has been to lead the charge for a cut in the top rate of tax, which surely would just been more cuts in public spending in some of the country’s most challenged areas.

Much of the political focus today will inevitably be on Mr Cameron. But how Boris handles himself when he flies in from Canada will matter too. Leadership really counts in these crisis situations.

Nobody has handled it well so far, but that matters less than how they handle it now. These are the moments that test leaders, and the public are very good at judging whether the tests are being passed.