An investigation is to be conducted into the death of a Polish man at Harmondsworth Immigration Removal Centre, The Independent has learned.
The 28-year-old allegedly hanged himself on Sunday afternoon and was taken to hospital.
The Home Office today confirmed that a man who had recently been held at the facility, near Heathrow airport, died yesterday in intensive care after life support was withdrawn.
A spokesperson had previously denied any knowledge of the incident, which comes in the same week the BBC broadcast undercover footage showing the alleged mocking and "choking" of detainees by guards at one immigration centre.
SOAS Detainee Support (SDS), who organise visits to immigration removal centres around London, said several detainees reported the death to them earlier in the week.
“Multiple people that SDS are in contact with have told us that a man from Poland hanged himself during lock-up after lunch on Sunday, and was taken away in an ambulance," a spokesperson told the Independent.
She added the incident had caused “unfathomable distress and anxiety amongst detainees in Harmondsworth and has contributed further to the creation of a toxic and harmful environment for the 400 men held in this centre".
She said: "Many SDS visitors have expressed strong concern regarding the people they are acting in solidarity with – some of whom have not slept or eaten properly since the harrowing incident on Sunday."
Charity Medical Justice, which works with detainees, also issued a statement, saying: "Clients have been calling us all week, traumatised by having seen what they say was a dead body, and terrified by their treatment and the conditions in immigration detention. Some fear they will die."
On Wednesday a spokesman for the Home Office told The Independent it was not possible they were unaware of the incident or had chosen not to release the details.
“I'm not saying I don't know. I'm saying an individual has not died at Harmondsworth. There's a big difference,” the spokesman said.
But today the department released a statement, saying: “We can confirm that a 28-year-old man recently released from Harmondsworth Immigration Removal Centre died in hospital after life support was withdrawn on Thursday September 7.
"Our thoughts are with his family at this very sad time. A full independent investigation will be conducted by the Prisons and Probation Ombudsman.”
SDS described the facilities, where people can be held for months or even years at a time, as "under the microscope this week" after the BBC broadcast a Panorama documentary Monday which included undercover footage from Brook House detention centre near Gatwick.
The secret filming showed a number of incidents including one which saw a G4S guard allegedly denying urgent medical assistance to a detainee who was “chewing his face off”, while a third custody officer was filmed allegedly confessing to assaulting a detainee by banging his head and bending his fingers back.
In response to the BBC film, G4S suspended nine members of staff and started an investigation. Jerry Petherick, managing director for custodial and detention services, said: “There is no place for the type of conduct described in the allegations anywhere in G4S."
“Such behaviour is not representative of the many G4S colleagues who do a great job, often in difficult and challenging circumstances, across the country.
“Once we have seen the evidence and concluded the investigation, I will ensure that we take the appropriate action,". he added.
There were nearly 400 recorded suicide attempts at UK detention centres in 2015, and there have been 29 recorded deaths since 1989.
The Independent reported in January that the number of EU nationals held in immigration detention has increased five-fold since the Conservatives came to power.
Mental health problems in detention are prevalent, with isolation and uncertainty compounding trauma detainees – many of whom are asylum seekers – may have experienced.
“[Undercover] recordings shine a light on these spaces that are otherwise completely hidden," an SDS spokesperson said.
"What is hard to make visible is the isolation and desolation that detention system seeks to instil in people.
"Through physical segregation from the outside world, as well as the entrenchment of a culture of disbelief and suspicion regarding those who are detained, people inside are stripped of their agency and made to feel entirely alone," the spokesperson added.
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