Iain Duncan Smith, the welfare secretary, has intervened in the row over the riots. In a sharp divergence from the "zero tolerance" message forwarded by Number 10, he said support for young people who want to leave gangs was just as important as tough sanctions for those who chose a life of crime.

Let's compare and contrast. Here's what David Cameron said on sentencing after the riots, in his speech in Witney on Monday:

Last week we saw the criminal justice system deal with an unprecedented challenge: the courts sat through the night and dispensed swift, firm justice. We saw that the system was on the side of the law-abiding majority.

And here is what Duncan Smith says in the Guardian today:

As senior police officers on both sides of the Atlantic have said, you can't just arrest your way out of this problem.

Duncan Smith's comments follow increasing disquiet from Liberal Democrats about the Tory reaction to the riots, which includes the suggestion that rioters be evicted from council houses or deprived of benefits. The question of proportionality of sentencing has not only caused friction within the coalition, but has also attracted criticism from legal professionals.

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