Prisoners most likely to reoffend are deliberately excluded from Justice Secretary Kenneth Clarke's rehabilitation revolution, a think-tank has said.
Three out of five criminals serving short-term sentences are convicted again within a year but Government plans to only provide literacy and numeracy workshops are "insufficient to achieve effective rehabilitation through employment", the Civitas report found.
It added that the Government pledge to only make training available to "offenders who have been punished and show a willingness to reform" will deliberately allow criminals who are most likely to reoffend to slip through the net.
Carolina Bracken, the report's author, said: "Whether it is because they are sentenced to a too short period of custody, because they fall outside Payment by Results incentives, or simply because the 'working prison' fails to provide a sufficient number of jobs, the very offenders who require the most intensive and individually-targeted intervention are those most likely to slip through the net.
"Unfortunately, this rehabilitative selection is not a new mistake. It is nonsensical to include only offenders 'who have been punished'.
"Prison should act as a punishment from the beginning of the sentence to the moment of release. There does not come a moment during an offender's spell in custody when it is appropriate for punishment to end. It is precisely these excluded prisoners who are at the highest risk of reoffending.
"If these offenders are not 'eligible' for rehabilitative work schemes, the Government's assertion that prison is less effective in reducing reoffending for certain groups of prisoners will continue to be a self-fulfilling prophecy."
A Ministry of Justice spokeswoman said: "We are committed to reforming our public services and reducing the cost of the justice system while protecting the public and punishing those who break the law.
"This Government inherited a system of spiralling costs and overly complex procedures - it's crucial that we rid the system of inefficiencies, ensure offenders face swift justice, and target interventions at those who will benefit the most.
"Many prisoners have significant literacy and numeracy issues which exclude them from the majority of jobs - that's why we're piloting intensive courses for short term prisoners which can be continued after their release or transfer."