Substantial improvements have been made to an immigration detention centre in west London declared "unsafe" by inspectors, the government has said.
Harmondsworth handles 12,000 failed asylum seekers a year
Harmondsworth Immigration Removal Centre near Heathrow Airport was found to have increasing levels of disorder in a report in September last year.
The Chief Inspector of Prisons found seven assaults a week took place there.
But Home Office minister Beverley Hughes says security has been stepped up and renovations are under way.
The centre, which opened in 2001, was originally expected to process 3,000 people a year who were due to be deported.
But the inspector's report said the centre was actually handling 12,000.
The increasing levels of disorder included damage and escape attempts.
But Ms Hughes said: "The centre today is very different to when it was first inspected.
"I am confident that, when completed, the on-going works at the centre and the changes that have been made will address many of the concerns raised in the report."
The inspectors had found there was no means of securing the centre in the event of a riot and there had been no health and safety assessment of the risks to detainees.
Ms Hughes said security has been stepped up, sprinklers installed and capacity is to increase from 345 beds to 500 beds.