Open-ended indeterminate sentences for the protection of the public (IPP) - currently being served by more than 6,000 prisoners in England & Wales - are ‘arbitrary and unlawful’, the European Court of Human Rights ruled today.

The Strasbourg judges said that many prisoners without release dates, in particular those with learning difficulties or mental health problems, had ‘no realistic chance’ of attending and passing rehabilitation courses to prove they were no longer a danger to the public and could be released back into society.

The unanimous ruling follows an appeal by three prisoners who had been held for almost three years longer than their trial judges had recommended. They were each awarded up to £6,500 in compensation along with £9,644 in costs.

Howard League for Penal Reform chief executive Frances Crook said: ‘The Howard League and many others have said for years that the IPP sentence was both wrong in principle and wrong in practice. It is wrong to imprison someone not for what they have done but what they might do.

‘In practice, the IPP has proved a disaster that has left many in a catch-22 situation where they can only be released from prison after completing courses that our overcrowded prisons cannot provide, not least because there are now over 6,000 prisoners serving IPP sentences.’

Prison Reform Trust director Juliet Lyon said the judgment should prompt justice secretary Chris Grayling to institute a review of the cases of more than 3,500 people held beyond their indeterminate sentence tariff dates and to use his discretion under new legislation to change the release test and ‘eradicate a stain’ on our justice system.

Lyon said: ‘It is shaming to have so many people locked up in our prisons, not for what they have done but for what they might do in the future. Many of these prisoners are condemned to years of uncertainty during which time they must somehow prove, from the confines of a bleak, overcrowded jail, that they no longer present a risk to the public.

‘The means to do this, attending scarce and not always reliable offending behaviour programmes, is barred to people with a mental illness, learning disability, many on medication and anyone with a low IQ score, trapping these most vulnerable people in a maze with no exit.’

New justice secretary Chris Grayling said he was disappointed by the judgment and intended to appeal against it. ‘It is not an area where I welcome the court seeking to make rulings,’ he said.