Up to 330 people are conducting a sit-down protest and hunger strike at an infamous detention centre.
Sources inside Harmondsworth removal centre told Politics.co.uk that hundreds of people were now sat in the outside court yard in protest at their conditions.
The detainees are refusing to move and only a handful of people with medical conditions are continuing to eat.
Security has started taking the ID cards from each individual involved in the sit down protest.
The detainees involved in the protest are on the C and D units in the centre, although they say they are receiving reports of solidarity actions in other parts of the facility.
Detainees agreed to launch the protest last night during dinner, as they shared their anger at the use of the fast track deportation programme, their treatment in the detention centre, a failure by authorities to give them their faxes and documents in time and an absence of adequate legal representation.
"The Home Office puts everyone on fast track," one detainee told Politics.co.uk over the phone.
"The health care here takes ages if a person is sick. A lot of people are waiting on travel documents - they're not even getting that.
"Someone was given a fast track for April this morning. This is May.
"They're not running detention. It's like prison over here."
Tensions at the centre mounted after a fax machine detainees were relying on for their appeals against deportation broke down and was not fixed for days, bringing their legal battles to a stand still.
One man on the sit-down protest has been on hunger strike for 67 days and is understood to be in extreme ill health.
Harmondsworth has a capacity of 615, making it one of the largest detention centres in Europe.
A report from the chief inspector of prisons last year found an increase in the number of self-harm incidents at the centre and a significant number of detainees refusing to accept food in protest at their conditions.
He said he was "concerned that immigration enforcement requirements were interfering with the contractor's attempts to focus on the care needs of some very sick and vulnerable individuals".
He also warned that elderly, vulnerable and incapacitated detainees, one of whom was terminally ill, were needlessly handcuffed in an "excessive and unacceptable" manner.
One man died shortly after his handcuffs were removed and another, an 84 year-old, died while still in restraints.
"These are shocking cases where a sense of humanity was lost," the chief inspector commented.