Conditions at an immigration detention centre in west London were “the worst” in the country – and so bad the chief inspector of prisons says he raised concerns with the then home secretary.

A report found Harmondsworth immigration removal centre near Heathrow Airport was “chaotic”, “truly shocking” and put detainees at “imminent risk of harm”.

The overcrowded facility was described by Charlie Taylor from the prisons watchdog as “decrepit”, with drug use and violence “widespread”. He said he contacted James Cleverly in March but neither Mr Cleverly nor his department had responded.

The Home Office said staffing levels had been increased since the inspection.

Mitie Care and Custody, which runs Harmondsworth, said occupancy rates had been affected by the closure of some parts of the centre for refurbishment.

The chief inspector’s letter to Mr Cleverly was prompted by report findings that conditions at the centre had worsened since the previous inspection.

The number of assaults had doubled, there had been several serious suicide attempts and cells had been doubled up to hold more men.

The watchdog also found if detainees refused to share an overcrowded cell, they were held in a separation unit until they agreed.

Staff largely kept to offices with “do not enter” taped across their doors, the watchdog warned.

Mr Taylor said: “The level of chaos that we found at Harmondsworth was truly shocking and we left deeply concerned that some of those held there were at imminent risk of harm.

“Nobody should be detained in an immigration removal centre unless they are going to be removed quickly from the country, yet around 60% of detainees were released from the centre, with only a third deported, which begs the question of why so much taxpayer money was being spent keeping them locked up in the first place.”

Mr Taylor wrote to the former Conservative home secretary Mr Cleverly on 12 March, after an inspection in February.

He said he “set out the many failures at the centre” but had “received no response”.

While the new director of Harmondsworth had a “good understanding” of many of the challenges faced by the centre and was “beginning to make good progress” in improving conditions, she will “need strong and consistent support at every level to succeed”, Mr Taylor added.

Kolbassia Haoussou, a refugee who fled torture in Africa and now works for charity Freedom from Torture, said he was held in Harmondsworth when he first arrived in the UK in 2005.

He said he knows “only too well how profoundly damaging detention can be” and called on the new Labour government to “rebuild a just asylum system that respects human dignity and the rule of law”.

Mitie faced challenges including staff shortages, the report said.

A “shambolic retendering process” led by the Home Office meant leaders had “no idea whether they would still be running the centre in the next few months”, according to the findings.

The contractual uncertainties had been a problem since last year, which made it “all but impossible to recruit permanent senior staff, who might only be in post for a matter of weeks”, the watchdog said.

Mitie said the company acknowledged the conditions and standard of care “fell below the level we would expect at this facility” when the inspection took place.

It said occupancy rates had been affected by the closure of some areas for refurbishment, adding: “This work is scheduled to be completed in August, following which a second wing (the conditions of which were particularly criticised by the inspection) will itself be closed for refurbishment.”

Mitie added the population demographic at the centre had changed and more than half of the residents now arrived from police custody or prisons, leading to an increase in disruptive behaviours and incidents.

However, the company said a “new staffing model” had led to “a material improvement” in staff engagement and retention.

The Home Office said: “It is vital that detention and removals are carried out with dignity and respect.

“The number of custody officers and dedicated welfare staff at Harmondsworth IRC has been increased since the inspection.”

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