Image caption Aerial cameras photographed detainees, believed to be protesting about living conditions, last March

Some detainees are being held for too long and in insect-ridden rooms at Europe's largest immigration centre in west London, inspectors say.

Conditions at Harmondsworth Immigration Removal Centre were "desolate", with bare rooms, broken equipment, bed bugs and cockroaches, the report by Chief Inspector of Prisons Peter Clarke said.

Some detainees were held for over a year, with one man held for five years.

The privately run centre said staff had been working to improve services.

The detention facility in West Drayton holds up to 661 men, including adult male asylum seekers, foreign offenders awaiting deportation and men who are in the UK illegally.

The inspector said "the direction of travel is now positive" for the centre but added: "It is unacceptable that conditions were allowed to decline so much."

The centre is run by private contractor MITIE Care and Custody on behalf of the Home Office, whose rules state detention in immigration centres should be used sparingly and for the shortest period necessary.

A Home Office spokeswoman said: "We take the welfare of our detainees extremely seriously and this report raises a number of important issues, which we are currently addressing."

'Substantial concerns'

The report found some men were held at Harmondsworth for an "unreasonably long" time, including 18 men who had been detained for more than a year and one man who had been held on separate occasions for a total of five years.

Among inspectors' "substantial concerns" were dirty, overcrowded and poorly ventilated residential units with a "desolate air", and unsanitary toilets and showers.

Nearly half of detainees said they had felt depressed or suicidal on arrival, but early days risk assessment processes were not good enough, despite an improved reception environment, the report said.

Shinda Bajwa, from India, told the BBC in 2014: "It is worse than prison. To be honest to you, I want to even go to prison, prison is better than this."

The secret world of the UK's immigration removal centres

Image caption Inspectors described overcrowded and poorly ventilated conditions at Harmondsworth

There was little positive engagement between staff and detainees and - despite some improvements - detainees still had problems in getting work, training and education, it added.

Some detainees were also segregated for too long and detainees who had been recommended for release by an independent panel or by doctors concerned for their mental health continued to be held at the centre, inspectors found.

Inspectors also made some positive comments, noting that the use of force was not high, the chaplaincy provided valued support and the centre had substantially improved preparation for release and removal of detainees.

The Home Office and its contractors have a responsibility to ensure this does not happen again Peter Clarke, Chief Inspector of Prisons

The report also praised the standard of the visiting system and said many detainees received support from the local visitors group, Detention Action.

Mr Clarke, who took over as chief inspector of prisons earlier this month, said standards at the centre had deteriorated while it was being run under a previous contract by GEO Group, which ended in 2014.

The recent unannounced inspection found many concerns dating back to the last inspection in 2013 had not been rectified and, in some respects, matters had deteriorated.

'Positive direction'

"The state of drift that we described in our last report has been arrested and the direction of travel is now positive," Mr Clarke said, but stressed that the ending of a contract should not also mean a drop in standards.

"The Home Office and its contractors have a responsibility to ensure this does not happen again."

Danny Spencer, a managing director for the immigration removal centre, said a programme of improvements was under way.

"This has continued in the six months since the inspection, addressing the recommendations and the operational and cultural challenges that we faced as incoming operator," he said.

A GEO Group spokesman said: "We are not commenting on the report on Harmondsworth as GEO has not been involved in operating the centre since 2014."

The spokeswoman for the Home Office pointed out MITIE is currently refurbishing the accommodation, and introducing better cleaning standards to the centre's healthcare facilities.

She also highlighted a review commissioned by the government last year to examine the welfare of those held in removal centres.

She said the Home Office was working on "significant reforms in relation to the mental health of detainees" and "ensuring there is a stronger focus on removal so that people spend the minimum amount of time in detention".