A prison has been criticised for detaining a female prisoner in segregation in a "squalid" cell for more than five years.

The discovery was made during an unannounced visit by the chief inspector of prisons, Nick Hardwick, to HMP Bronzefield women's prison near Ashford, Surrey.

In the inspection report, Mr Hardwick said: "We were dismayed that the woman who had already been in the segregation unit for three years in 2010 was still there in 2013. Her cell was unkempt and squalid and she seldom left it."

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Mr Hardwick said her prolonged detention in the segregation unit amounted to "cruel, inhumane and degrading treatment - and we use these words advisedly".

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

Despite successfully tackling a range of challenges thrown up by its "complex population" of inmates, the prison still faces issues that need to be dealt with at a national level, Mr Hardwick said.

The way women were transported to and from the prison was also unacceptable, according to the inspectors. Women were carried in vehicles containing men and spent long periods in the van, possibly because they had to wait while male prisoners were dropped off first, and some complained they felt unsafe during the trip.

Frances Crook, chief executive of the Howard League for Penal Reform, described the case as "shocking" and said the woman's treatment "appears to amount to torture". Cases such as this happening in an English prison "should shame ministers who tolerate the over-use of custody for women and consequent poor treatment," they added.

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

There are 446 women on remand or serving sentences ranging from a few weeks to life at the prison. It has a small number of "restricted status" women, some of whom have severe personality disorders.

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HMP Bronzefield is run by Sodexo Justice Services. The report calls for a policy to help manage women "with complex needs who cannot be supported in the prison's normal location". This should include providing a humane and properly resourced environment and regime for those women, as well as for restricted status women in this category, it says.

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

Practical resettlement services were rated very good, but could be helped by better co-ordination of offender management, and work to support women in keeping strong relationships with their families was underdeveloped, the report said.

In contrast, the inspectors ranked the reception, first night and induction arrangements as good across the board and there was very good support for women with substance misuse problems throughout their prison stays.

Support for those with alcohol problems was particularly impressive and there had been no self-inflicted deaths at the prison and the number of self-harm incidents had reduced dramatically year on year, it was found.

The most vulnerable women got sensitive but effective support and the staff had a good knowledge of the women in their care.

Much-improved health care and being allowed a reasonable amount of time out of the cells, along with different activities, were also among the positives identified by the inspectors.

The inspectors said the areas which remain of most concern are outside the prison's direct control.

The inspection took place whilst the Government was conducting a review of the women's custodial estate. Mr Hardwick said: "HMP Bronzefield illustrated some of the challenges the review would need to address.

"It is a credit to the managers and staff at Bronzefield that they meet these challenges as well as they do. There is more that can be done locally, but some of the issues identified in this report require a fundamentally different approach to the imprisonment of women at national level."

Michael Spurr, chief executive of the National Offender Management Service, said: "This report shows the good work that the director and her staff are doing with the complex population at Bronzefield.

"I am pleased that the chief inspector recognises the very good support that is being offered to the women, which is helping to play a key role in their rehabilitation.

"I recognise the importance of looking at our national approach to women in prison and a review was commissioned earlier in the year into the women's custodial estate, the outcome of which will be announced in due course."

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 five 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."

Additional reporting by Press Association