An "unofficial" punishment wing that fails to meet minimum prison service standards has been operating at Liverpool jail, the chief inspector of prisons has disclosed in a report on Friday.

Nick Hardwick said that prisoners sent to the wing as a result of the jail's policy of zero tolerance to bad behaviour were banned from mixing with other prisoners for 14 days, not allowed to work, and banned from having a radio.

The chief inspector's report on the prison, known locally as Walton jail, said the newly created "reintegration" unit on the first floor of J-wing operated a regime that was too punitive and too restrictive.

The report, which followed an inspection carried out in December, found that some of those in the unit were vulnerable inmates at risk of suicide, and that in some cases little effort had been made to identify the reasons for the prisoners' bad behaviour.

"The incentives and earned privileges scheme had been used to reinforce a zero-tolerance approach to a range of bad behaviour," said the report. "In practice, this was too often used as a crude punishment system with little emphasis on encouraging good behaviour. Of most concern was the designation of one wing landing as a 'reintegration unit' where prisoners on the 'basic' level of the scheme were held."

Hardwick said the unit was similar to a segregation unit, but without the procedural and other safeguards that segregation would require: "In some aspects, the unit did not meet the minimum standards required by the prison service. Prisoners were not allowed association for the first 14 days they spent in the unit and, until the inspection, were not allowed a radio."

The report said that prisoners in the unit were only allowed to attend gym once a week and chapel services. It added that the use of this "basic regime" unit seemed a subversion of formal disciplinary procedures with inmates confined to cells with no safeguards.

"One reason given for placing a man on basic was he was 'alleged to have assaulted another prisoner' but there was no evidence from his [prison] record or security file to support this and he had not been subject to a disciplinary charge."

Hardwick said: "The challenge of making the improvements that HMP Liverpool requires should not be underestimated. There is still a need for significant improvements, and some aspects of the regime ? particularly the treatment of vulnerable prisoners and those on the basic incentives level ? are unacceptable. However, overall this inspection found improvements were being made and the prison had some encouraging plans for the future, although they were still too new to be judged."

Michael Spurr of the National Offender Management Service said the governor and his team would address the areas of concern highlighted by the report.