After nearly six years running Britain's highest-profile mental institution, the head of Broadmoor high security hospital is to stand down.

Dr Julie Hollyman, who became the first female chief executive of West London Mental Health Trust in 1998, says she will quit the job - which includes responsibility for Broadmoor - at the end of this year, adding that it had not been "an easy decision to make".

"I believe it would not be good for the trust if I remained as chief executive until retirement age," said the 52-year-old, in an official memo issued to staff.

"As I'm not getting any younger I think I need to do it now. It's best to be absolutely open about my intentions and allow the recruitment of my successor to begin."

West London Mental Health Trust said that Dr Hollyman, who earns more than £80,000 a year, had been considering a change of job for at least two years. They also said that they had already started looking for a replacement.

Her resignation comes three months after the hospital was at the centre of allegations by a whistleblower that female inmates had been sexually abused at Broadmoor. Julia Wassell, the former director of women's services, complained to management after carrying out a survey of 28 women on their experiences over three years.

This revealed a catalogue of serious abuse including 1,008 incidents of verbal abuse, 64 cases of sexual harassment, 56 cases of sexual abuse, five rapes and six incidents of consensual sex. In addition, several women asked for pregnancy tests.

Ms Wassell said some of these incidents took place after Dr Hollyman was appointed as chief executive. The trust settled Ms Wassell's claim without admitting liability, and all mixed-sex activity was suspended at the hospital after an independent review in March 2002.

The Commission for Health Improvement, an independent body set up to monitor and improve NHS services, is currently carrying out a review of Broadmoor as part of a routine assessment of all mental health services provided by West London Mental Health Trust.

This will be published in November this year and will examine the treatment provided for patients and how staff are working to improve the services. It will also highlight areas for improvement.

The Independent On Sunday is campaigning for better treatment for the mentally ill, including those held in secure hospitals. This paper has highlighted the plight of hundreds of patients wrongly incarcerated in secure hospitals who cannot be moved because there are not enough beds for them in medium-security units.

The Department of Health has already announced that Broadmoor's women's facilities will close over the next two to three years and patients will be transferred to a new women-only facility at Rampton special hospital in Northamptonshire.

Patients held in secure hospitals have faced increased security clampdowns in recent months under a raft of draconian measures introduced by the Government.

These include staff being told to swab patients' mouths for traces of alcohol and to take hair samples to determine whether or not they have used illicit drugs.