Detainees have been held for up to five years with long spells in segregation and dirty accommodation at Europe’s largest immigration detention centre near Heathrow, inspectors say.
Chief Inspector of Prisons Peter Clarke said conditions at Harmondsworth Immigration Removal Centre had deteriorated since its last inspection and there were concerns across most areas.
Their report found 18 detainees had been held for over a year and one man had been detained on separate occasions adding up to a total of five years.
Mr Clarke said it was "unacceptable that conditions were allowed to decline so much towards the end of the last contract" when the centre was run by GEO Group.
Management of the centre in West Drayton was branded "deplorable" last night by campaign group Detention Forum, who called on the Government to impose a time limit on immigration detention.
The centre, which holds up to 661 men, has been run for the Home Office by the Mitie Group since September 2014.
But the unannounced inspection last September showed many concerns dating back to 2013 had still not been rectified and in some respects, things had deteriorated.
Inspectors singled out the "appalling" state of some of the residential units as a sign of lack of investment from the previous contract.
Some newer accommodation was dirty and rundown, while many toilets and showers in the older units were seriously insanitary with many overcrowded, poorly ventilated rooms, the report said.
Mr Clarke said: "The Home Office and its contractors have a responsibility to ensure this does not happen again.
"Following the inspection, we were informed by the Home Office that lessons had been learned and that a new set of principles were established to prevent a recurrence of this situation. We will assess the success of these measurements in due course."
Danny Spencer, a managing director of the centre, said: "We are encouraged that the efforts of our people and partners have been recognised.
"The inspection also identified things we need to do better. We were aware of most of them and have been working on an improvement programme since we commenced the service.
“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."
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.”
