Compensation claims worth millions of pounds could be filed against the Prison Service for the unlawful imprisonment of thousands of former inmates.

The prospect of mass legal action by ex-prisoners arose when the European Court ruled it was illegal for prison governors to extend inmates' sentences as a punishment for bad behaviour.

As a result, about 900 prisoners in England and Wales were being released immediately or in coming days, said the Home Office.

Damages claims will run into millions of pounds from prisoners who were illegally detained

Prison Reform Trust

The Prison Reform Trust said the Prison Service had ignored several warnings that it was breaking human rights law.

"As a result they now have to release hundreds of prisoners and face damages claims which will run into millions of pounds from prisoners who were illegally detained."

A Home Office spokesman said: "If the prisoners want to take legal action against the Prison Service that's up to them individually."

'Minor offences'

Criminologist David Wilson said the ruling was "embarrassing" for the government and the Prison Service, but was sceptical that prisoners would be able to sue successfully.

"Clearly there is going to be some kind of vulnerability of the Prison Service in relation to compensation, but I would suggest that it might be more difficult than is being implied... for one thing I'm sure governors were acting in good faith."

The historic ruling stripped governors of powers introduced in 1991, allowing them to add up to 42 days to a prisoners' sentence.

The court said the punishments, used for offences like drinking alcohol or using drugs, violated the inmates' right to a fair trial.

Both Mr Wilson and the Prison Reform Trust said days were often added for offences which would not even attract a fine in the courts - such as being rude to a warden, or stealing extra food rations.

Governors 'mixed'

Prison governors gave a "mixed" reaction to the ruling and said they would hold talks next week to decide what other sanctions to use to keep order.

David Roddan, general secretary of the Prison Governors Association, said measures such as taking away a prisoner's television rights for bad behaviour had been effective in the past.

He did not think the ruling would necessarily make enforcing order more difficult, saying there had been no increase in disorder in Scottish jails, which ditched additional days a year ago.

The Times newspaper reports that among the prisoners being released are one dangerous category A offender and at least four inmates from top security prisons.

Scotland

The Strasbourg cases involved Okechukwiw Ezeh, who was charged with using threatening language to a probation officer, and Lawrence Connors, who was charged with assault of a prison officer.

Judges said Ezeh's sentence of an extra 40 days and Connors' term of an extra seven days' detention violated Article 6 of the European Convention on Human Rights because they had been denied the right to a fair trial.

Prison governors in Scotland lost their power to add extra days to prison sentences in June 2001 because the Scottish Executive anticipated possible problems in the European Court of Human Rights.

Mr Wilson said the Prison Service may have a legal difficulty explaining why it continued with the punishment when its Scottish counterpart had ended it.