Anne Owers has attacked the use of special cells at Styal prison in an inspection report that reveals how several women were stripped under restraint and placed in bare cells on the segregation unit.

The chief inspector of prison's criticisms follow the revelation earlier this year that special cells had been used 154 times for juveniles in 13 young offenders institutions.

This was despite earlier claims by the Home Office that there was only one cell used for this age group (news, page 6, 15 January).

At the time, the Howard League for Penal Reform condemned the use of the cells for vulnerable young people, and Owers pledged to monitor the use of the cells, describing them as an "extreme sanction".

In her latest report, Owers says she is "particularly concerned" about the frequency and length of use of the special cells for women and young offenders restrained in the Cheshire jail.

"Women were held for lengthy periods - an average of seven and a half hours - sometimes long after records showed that they had calmed down," she says. One in 10 were held for more than 12 hours.

The inspector also expressed concern at the use of the cells for self-harmers, which is against Prison Service guidance.

The report reveals that the "extreme facility" was used 44 times in the year before inspection and that, in 11 cases, no reason was given for placing the women there.

She highlights several instances where women were stripped under restraint and placed in the cells. However, there was no recorded risk assessment and no use of alternative measures.

Owers reiterates her belief that special cells should be a facility to allow people to calm down and not be "a long-term holding facility".

Frances Crook, Howard League for Penal Reform director, attacked the use of cells as "completely inappropriate for women".

She called for the head of the Prison Service to write to the courts telling them not to send women to Styal as it was unsafe.

There have been six self-inflicted deaths at Styal in 18 months.