The Sketch: All the talk is of crime and punishment from the serial repeat offenders

You'd think they'd blush to do it, frankly. Standing up in a public place and pontificating about "repeat offending" and "anti-social behaviour", as if there was not the remotest possibility that the words might splash back in their face.

The sad truth is if you want to see recidivists glorying in their refusal to mend their ways, there are few better places than the Commons during Home Office questions.

"At it again", you think wearily – as some loyal backbencher stands up to rub emollient into David Blunkett, or an opposition hoolie tries to get a punch-up under way. I mean, this talk about rehabilitation and "acceptable behaviour contracts" is all very well – but some of these people just don't want to change. They are institutionalised

According to Hilary Benn 71,360 people were in prison as of yesterday morning – and nobody seems entirely sure whether that number should be bigger or smaller.

On the one hand, marinading young men in a concentrated solution of criminality is not a good way to conscript them into the great stakeholder society. For that, they really need to be released into somebody else's council house as soon as possible. On the other hand, there are far too many stakeholders out there who really should be inside – David Blunkett mentioned the rather worrying drop in rape convictions as just one example, while Tony Banks was fretful about the unknown assassin who had shot one of his constituents the other day and who is still at liberty.

It's possible, I suppose, that this man had signed an "acceptable behaviour contract" and not quite understood the small print. He may need to have it explained to him that gunplay is not really a tolerable method of conflict resolution. Either way, it doesn't make it easier to decide whether the prison population is shockingly high or shockingly low. It must go up, and it must come down – and ideally both at the same time.

Oliver Letwin was preoccupied with another arithmetical conundrum – one he lumbered towards in an uncharacteristically ponderous manner. The Government was bent on promoting drug awareness, he said approvingly, but in practice hadn't they simply promoted the awareness among drug dealers that Brixton was a very good place to do business? John Denham looked disappointed with this leaden bit of word play – a bit like a probation officer whose client has just phoned him from the local nick. This wasn't the responsible behaviour he'd been hoping for. But Mr Letwin wasn't chastened. The Home Secretary had promised to double the maximum sentence for cannabis dealing, he pointed out, which, cannabis being a Class B drug, would come to 14 years. But if the Government reclassified cannabis as a Class C drug the doubled sentence would be only 10 years. This isn't a contradiction at all if you think about it for a couple of seconds. The sentence goes up either way. But Mr Denham didn't have a couple of seconds and he began to stammer like a man three hours late for his crack pipe refill. Mr Letwin should "concentrate on the issues of substance", he said, "rather than juggling with figures". In other words – stop being so damn specific and get back to the standard clichés; I know how to handle those.

Simon Carr returns tomorrow