Staff at an immigration removal centre near Heathrow Airport feared for their lives and locked themselves inside panic rooms as more than 100 armed detainees rioted with makeshift weapons and set fire to common areas, it was claimed last night.
Rita Biddulph, who works with the Home Office's independent monitoring board, alleged there are seven units within the Harmondsworth Immigration Detention Centre in West Drayton, Middlesex, each housing 28 detainees and assigned just two staff members.
In the early hours of Saturday, a power outage led to a blackout and automatically opened electronically locked doors to migrants' cells. Violence erupted shortly thereafter and peaked at about 2am. None of the staff, nor detainees, were injured.
As the detainees found makeshift weapons - including smashed up tables and chairs and the metal slats from under their beds - terrified staff retreated into manually lockable safe rooms and called riot police for backup.
Ms Biddulph told The Sun: 'Inside each unit there is a safe room, which is manually lockable. Because there were more detainees than staff, they had to lock themselves in panic rooms for their safety.'
It comes as Minister of State for Immigration Robert Jenrick vowed to 'swiftly' deport any detainees who took part in the riots. He promised that the 'perpetrators of this disturbance will be held to account'.
Images from the scene show multiple police officers outside the centre along with police vans.
The centre is known as Europe's largest detention facility and can house up to 670 men. The Home Office could not confirm exactly how many detainees are currently in the centre, nor provide exact figures on how many were involved in the riots.
A source at Harmondsworth told the publication 'it was chaos' when the power went out, cutting off lighting and heating for hours.
'The migrants got angry,' the source said. 'The decision for them to gather in there could have saved lives, It certainly prevented injuries.
'Tensions boiled over because migrants did not know what was going on and it was pitch-black... All the staff were panicking. The situation only started to come under control when riot police went in.'
Mr Jenrick said in a statement: 'There was disruption overnight at Harmondsworth Immigration Removal Centre after a loss of power. Thankfully no staff working or individuals detained there were hurt, despite clear evidence of unacceptable levels of violence and disorder.
'The priority now is to move people to other centres while engineers fix the power fault and repair any damage.
'The public should be reassured that offenders and others waiting removal from the UK are being held securely. The perpetrators of this disturbance will be held to account and, where appropriate, removed from the country as swiftly as is practicable.
'The Home Secretary and I have been kept abreast of events throughout the night and today by our hard-working teams. I have also visited the site today and I expect the centre to be empty by the end of the day.
'I am grateful to Home Office staff, contractors and officers from HMPPS and the Metropolitan police for their professionalism and practical support.'