I thought David Cameron was made of sterner stuff. His claim yesterday that having to agree to give prisoners the right to vote had made him “physically ill” was a surprising admission for a prime minister who will have to face some really tough decisions with profound effects on many people in the future. It also gave an insight into one of the reasons that Britain has such a poor record in rehabilitating prisoners.

There are three main purposes in prison sentences: the first is to safeguard society from someone found guilty of a serious crime; the second is to punish that person appropriately; and the third is to rehabilitate prisoners so that they can be returned to society without risk of committing further offences.

The rehabilitation part is the most difficult part and it is a regrettable fact that in Britain too many prisoners are set free in a mood to take revenge on society because of the dismissive and diminishing way in which they have been treated. There is no law which says that only a person of good behaviour should be permitted to vote. To deprive prisoners of the vote is to tell them that their future place in society has already been determined. Britain's refusal to accept a 2004 European Court of Human Rights ruling on this matter lies behind Mr Cameron's decision -- but taken to avoid the cost of further resistance, not on principle.