An immigration removal centre has been hit by surging levels of violence and drug use, an inspection report has warned.
Morton Hall near Lincoln has seen a "significant decline" in safety, with rising numbers of assaults on detainees and staff.
An official watchdog raised concerns about the impact of new psychoactive substances (NPS) - drugs previously known as "legal highs".
IRCs are used to house foreign nationals including overseas offenders and asylum seekers either while their cases are decided or after their leave to remain in the country has been refused.
Morton Hall is operated by HM Prison Service on behalf of the Home Office and holds up to 392 men. It had been a women's prison until 2011.
HM Inspectorate of Prisons (HMIP) visited the centre in November and concluded that, although it was generally well run, safety had worsened since the last inspection in 2013.
The number of violent incidents at the centre had risen by two-thirds. There had been 38 detainee-on-detainee assaults and 11 on staff in the previous six months.
Self-harm incidents had also risen and there had been a self-inflicted death since the last inspection, while another man died after the latest visit.
The HMIP report noted that there had been a "concerning" number of security incidents at the centre, including 16 incidents where detainees had set fires in cells or in communal areas on residential units.
There was at least one escape attempt where a detainee managed to get through his cell window and into the grounds before he was captured at the perimeter fence.
There was also "strong evidence" of a "serious increase" in the availability and use of NPS.
The drugs have been identified as a factor in the recent unrest that has swept through the prison system.
Chief Inspector of Prisons Peter Clarke said he was repeatedly invited to ascribe the rise in violence and other disruptive behaviour to a change in the profile of the detainee population, with half of those held at the centre now ex-prisoners.
Mr Clarke said: "Members of staff suggested to me that this has had a negative impact on the safety of the centre, but the evidence for this assertion was not available without more research and analysis."
The watchdog found that too many detainees were held for prolonged periods - 31 for over a year - and the average length of detention was high, at over three months.
In the previous six months, 293 detainees had been removed from the country, 553 were released, and 1,317 had been transferred to "other places of detention".
The third figure could include people who are removed from the UK after being transferred to other facilities from Morton Hall.
Mr Clarke added: "The very real challenges faced by this IRC should not be allowed to overshadow the commitment and skill of the staff who clearly had the interests of the detainees at the forefront of their minds."
A Home Office spokeswoman said: "We are pleased that HM Chief Inspector of Prisons has recognised that Morton Hall is generally well run, and that staff relationships with detainees are strong.
"Detention is an important tool that helps us remove those with no right to be in the country and it is vital that all our facilities are safe and secure.
"Strategies to reduce incidents of violence and self-harm, and to reduce use of psychoactive substances, are already in place and will be kept under constant review.
"Nobody is detained indefinitely and regular reviews of detention are undertaken to ensure that it remains lawful and proportionate. There is a clear presumption that vulnerable people should not be detained.
"An action plan is being implemented in response to the Chief Inspector's recommendations."
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