When governments have bad weeks there are various groups that should brace themselves for trouble: ministers obviously, special advisers almost certainly, civil servants more than likely.

But perhaps we should add to that a more unlikely section of society: those serving sentences at Her Majesty's pleasure.

Prisoners, never the most popular group in society, would appear to be ideal whipping boys for governments on the run.

After a difficult week, capped by the resignation of the Chief Whip, Downing Street spin went into overdrive and helped to produce yesterday's Mail on Sunday front page headline: CAMERON: IT'S TIME TO MUG A HOODIE.

In the trail for David Cameron's speech today, a number of tough measures were floated including the possibility of axing the discharge grant of £46 given to prisoners on release, a lifeline that helps many while they wait to receive benefits.

Given the fact that only last week the Office for National Statistics confirmed that recorded crime was at its lowest level since 1986, it seems bizarre for the government to respond by calling for tougher sentencing.

It is perhaps unsurprising then that the speech itself appears to be quite distant from the picture provided to the Mail on Sunday, being a rather reasonable exposition of the government's policies and the Prime Minister's desire to see a 'rehabilitation revolution'.

In particular, David Cameron talks about extending a payment by results approach currently being piloted so that prisons and providers are paid to reduce reoffending.

Assuming that the government is not set on undermining rehabilitation by doing something as foolish as axing the discharge grant, then the government's 'tough but intelligent' approach to criminal justice should not be dismissed out of hand. There are, however, some thorny issues which the Prime Minister has not addressed today.

Firstly, it is all very well to pay providers by results but you must have a result that is meaningful in the first place.

The Ministry of Justice is looking at paying providers on whether individuals are reconvicted or not but this is a blunt measure that does not reflect the reality of how people desist from crime. Rather than simply shift from offending to not offending like an electrical switch, people who offend tend to lead chaotic lives and slip in and out of trouble with the law.

Sometimes progress is better measured in whether people are reoffending less seriously or less frequently than before. But that kind of progress would not be measured under current proposals, which raises questions as to what success any providers will be able to produce.

Secondly, there are worries that many of the small voluntary sector organisations currently working in prisons and probation will be unable to survive in a payment by results environment.

Large providers able to partner up with the likes of Serco and G4S are more likely to thrive in what will inevitably become a cutthroat market.

Perhaps the most important issue however is what a truly tough and intelligent look at the penal system would involve. The Ministry of Justice is facing 6 per cent cuts year on year and has a spending gap which was created by the collapse of sentencing reforms which the previous

Justice Secretary Ken Clarke tried introducing to reduce the prison population. It estimated, for example, that the agency running prisons and probation will spend £32 million more than its budget for 2012-13 due to the lack of progress in reducing prison numbers.

At the same time the reoffending statistics which so exercise David Cameron tell their own story. Almost two thirds of those serving sentences of a year or less go on to be reconvicted within two years of release, demonstrating that the revolving door between prison and the community is spinning fast. Worse, each spell in prison makes reoffending more likely. By contrast, the reoffending rate for much cheaper community orders is 37 per cent, falling to 34 per cent for those on intensive programmes tackling drug and alcohol misuse.

When the Howard League interviewed prisoners as part of a research project into short sentences, many told us that they preferred spells in prison which ask little of them compared to the challenges they would face completing community programmes that directly tackle the causes of offending.

Given the Ministry of Justice is hurtling towards a fiscal precipice, a truly tough and intelligent approach would be to reduce prison numbers and focus on effective interventions in the community, with a better use of scarce resources within prison walls. Yet there was no sign of any of this in the Prime Minister's speech today.