A British prison has been criticised for holding a female prisoner in a "squalid" segregation cell for more than five years, which campaigners have said amounted to torture.

The woman was found during an unannounced visit by prison inspectors to HMP Bronzefield near Ashford, Surrey, in April.

A report by the chief of prison inspections Nick Hardwick described how inspectors were "dismayed" to find that one prisoner who had already been in the segregation unit for three years in 2010 was still there when they arrived again in 2013.

Hardwick described her cell as "unkempt and squalid" and said that she was seldom allowed to leave it. He said her detention amounted to "cruel, inhumane and degrading treatment - and we use these words advisedly".

"Although more activities had been organised for her and better multidisciplinary support was available, she still had too little to occupy her," he said.

Hardwick said the treatment and conditions of other women held for long periods in segregation was "little better".

He said: "Much of this was outside the prison's direct control and required a national strategy for meeting the needs of these very complex women - as exists in the male estate.

"However, Bronzefield itself needed to do more to ameliorate the worst effects of this national failure."

A small number of the 446 prisoners at Bronzefield suffer from severe personality disorders. The report recommended introducing a policy to help manage women "with complex needs who cannot be supported in the prison's normal location".

The report identified the need for a fundamentally different national approach to the imprisonment of women.

Amount to torture

The report said transporting female prisoners was an example of where change was needed. Women were carried in vehicles with men and spent long periods in the van. Many women said they felt unsafe.

Frances Crook, chief executive of the Howard League for Penal Reform, said: "This shocking case of treatment, which appears to amount to torture, should shame ministers who tolerate the overuse of custody for women and consequent poor treatment.

"Her Majesty's chief inspector is absolutely right that specialist care outside the prison needs to be developed for the handful of women who pose particular challenges."

Juliet Lyon, director of the Prison Reform Trust, said: "The chief inspector reports that staff are doing their best to respond to the needs of women at Bronzefield, many of whom are in poor mental and physical health, addicted to drugs and drink, and traumatised by separation from their children.

"But why in this day and age are women with such complex needs transported like cattle and dumped in prison, where one of the most damaged women is left to rot in some form of solitary confinement for six years?

"We are quick to condemn cruel, inhumane and degrading treatment of people in prison in other countries, now government must act to put right failings in our own women's justice system."