John Rentoul: Dave and Tone's hug-in... they're tough on hoodies, tough on the causes of hoodies

Who can blame Reid for trying to shock the Home Office into shape

We all believe contradictory and therefore impossible things - six before breakfast seems a rather modest accomplishment. The White Queen in Through the Looking Glass was not really trying. Two of the views commonly expressed in recent weeks, sometimes by the same people, form a natural pair. One is that we put too many people in prison in this country. The other is that it was a culpable failing on the part of Charles Clarke, the former home secretary, to let people out of prison without considering them for deportation.

Both views seem reasonable on their own. Michael Howard's slogan, "prison works", was crass. Prison only works in the crude sense that criminals cannot commit crimes - against the rest of us, at least - while they are in jail. When they come out, they are more likely to commit crimes than they were before they went in. So, unless sentences are so long that they cancel out the effect of prison in preparing criminals for a life of crime, prison does the opposite of working.

However, it was also a bit surprising that foreign nationals were simply waved out of the prison gates with a "Mind how you go" at the end of their time served. The liberal newspapers joined with enthusiasm in saying that they should all be put back in jail until immigration tribunals could be got together to put them on planes out of the country.

The White Queens have led the responses to last week's plans from John Reid for more reforms of the criminal justice system. Politician criticised judge for a "too lenient" sentence. Judge said law made by politicians gave him no choice. Politician said, "Right, we'll change the law to give you more discretion." Is everybody happy? You bet your life they ain't.

And, of course, Reid's plan to increase the number of prison places is not the answer to crime. But reducing the number of prisoners is even less of the answer. It would obviously be desirable to have fewer people in prison, but only as a result of lower crime or the miraculous invention of an offender management programme that reliably reduces re-offending. That was Tony Blair's revolutionary insight as shadow home secretary in 1993: until you start dealing with the causes of crime, you have to be prepared to see the prison population rise.

Now David Cameron has caught up to where Blair was 13 years ago. His suggestion that what teenage hoodies need is love and understanding is, in effect, the second half of Blair's slogan: "Tough on the causes of crime". That was the "Labour" half, and Cameron gains a similar shock value from endorsing it to that gained by Blair in endorsing the "Tory" half: "Tough on crime". Our poll today confirms that young voters are particularly impressed by the hug-a-hoodie message.

The trouble is, as I remember Howard saying through clenched teeth at the time, "We are all interested in the causes of crime; no one knows what the causes of crime actually are." As home secretary, he was heartily sick of the press gooing over golden-boy Blair's brilliant slogan.

He had a point, though. After nine years of a government dedicated to being tough on the causes of crime, the overall level of crime may have fallen, but it started to fall under a government that was not explicitly committed to this principle, when Howard himself was in charge. Worse, the most recent statistics suggest that the fall may be bottoming out, and that violent crime, which is what people are really afraid of, has increased.

Yet this is a government that has hugged hoodies more energetically than any before. Sure, it has slapped Asbos on them (the "tough on crime" bit), but it has also pumped money into Sure Start, early years education and primary schools (the "tough on the causes" bit). The Labour backbenches enjoyed themselves last week when Blair and Sir Gerald Kaufman made fun of Cameron's hoodie speech.

For all the criticism of the House of Commons for encouraging adversarial politics, both sides like nothing more than launching raids deep into each other's territory. The Tories did it on the Education Bill, offering mocking support for trust schools; Labour MPs enjoy strutting their "tough" stuff.

The real core of the fight against crime, though, is the causes bit. It is difficult, diffuse and long term. The slogans are easy, the work of moments. The policies are impossible, with results that may not come through for a generation. We all know this, but we are White Queens. We complain that the Government has had nine years to solve the causes of crime when we know that the modest progress that has been made may be near the limits of the politically possible unless a country has the social discipline of Singapore. We acknowledge the deep-seated problems of drugs and of disordered families, and the fragility of the levers that liberal democratic states can pull, and yet demand quick results.

Blair will pursue this theme, in his continuing role as seminar facilitator to a nation of White Queens, in a speech this week about the limits of the state.

I am told that he will take up one of his favourite complaints about the press; that it will demand on one page that something must be done while condemning the interfering nanny state on another. One of the questions he will ask will be what the Government's role should be in obesity, the subject of one of his more memorable lines two years ago: "I am responsible for many things but I can't make people slimmer."

We complain about politicians who can expect to be in a job for perhaps two years being focused on the short-term and the shiny. Yet who can blame Reid, who knows that his post-Blair prospects are far from assured, for using symbolism and what might be called visible policing to try to shock the Home Office into some kind of better shape?

The challenge of crime policy is to describe what comes next. Both the parties now agree that we must be tough on hoodies and tough on the causes of hoodies. We ought to know, after nine years, how difficult both parts of that policy are.

Cameron has got to the place where Blair used to be - but what lessons do our future leaders draw from the successes and failures of a policy that over the past nine years has become the consensus ?