Ministers and private firm G4S have been accused of attempting to "cover up" the true scale of recent disturbances at the country's largest prison.
Trouble broke out on a wing at G4S-run HMP Oakwood, near Wolverhampton, at 5pm on Sunday evening and was not resolved for nine hours until 2am yesterday, the Ministry of Justice and G4S said.
However, conflicting accounts have emerged over what actually happened at the 1,600-place jail, while fresh reports suggest further violent incidents have occurred at the prison in the months before the most recent outbreak of disorder.
HMP Oakwood, a category C prison, was the scene of a number of rooftop protests last year and was slammed by inspectors during a surprise visit.
Sadiq Khan MP, Labour's shadow j ustice secretary, said: "More and more information is coming to light that suggests the Ministry of Justice and G4S are trying to cover up the true scale of the disturbances in the Justice Secretary's flagship Oakwood prison on Sunday night.
"The Tory-led Government needs to come clean and admit what really happened, and acknowledge that there are some very serious underlying problems at Oakwood. The prison is not punishing and reforming offenders anywhere near as well as it should, and the taxpayer deserves better.
"This isn't an isolated incident. Since opening the prison has been plagued by rooftop protests, disturbances and a damning Chief Inspectors' Report that revealed inmates found it easier to get drugs than soap. Yet instead of getting a grip, Chris Grayling praises Oakwood as his model for the rest of the prisons system."
Yesterday in a joint statement, the MoJ and G4S said the incident, which took place in one wing of the jail, involved up to 20 inmates, who threatened officers and damaged cells and prison property. No prison staff were injured, although one prisoner has been treated for minor injuries.
They denied reports that prison staff had been taken hostage, labelling such claims as "completely untrue".
"The safety of our personnel and those prisoners in our care is our top priority, and we are grateful to our colleagues who were able to help us bring the incident to a close safely, and effectively," the joint statement said.
"Established incident procedures were followed correctly and worked as they were meant to.
"As an investigation has now commenced into the reasons for this disruption, as well as a criminal investigation, it would be inappropriate to comment further at this time."
Standard procedures were initiated to deal with the incident after the MoJ was informed, with rapid response teams deployed. Staffordshire Police were also informed.
The prison - the largest in England and Wales - opened in April 2012 as a training prison next to the existing HMP Featherstone and HMP Brinsford near Wolverhampton.
In a report published in October, HM Inspectorate of Prisons (HMIP) reported inexperienced staff and high levels of violence and self-harm at the jail - dubbed ''Jokewood'' by prisoners.
Chief Inspector of Prisons Nick Hardwick warned there were ''real risks if matters were allowed to drift'' at the prison.
At the time G4S said improvements were being made but admitted launching the prison was a "complex and challenging operation".
G4S - well-known for its botched handling of its Olympics security contract - has been under review by the Government following revelations it overcharged for criminal-tagging contracts.
The Government has since announced that electronic monitoring will handed to another firm on an interim basis at the end of the financial year.
Controversy around HMP Oakwood comes as the majority of Wrexham council's planning committee approved outline planning permission for a £250 million super-prison which will have a 2,000-inmate capacity.
Juliet Lyon, director of the Prison Reform Trust, said: " Slashing prison budgets while warehousing ever greater numbers overseen by largely inexperienced staff is no way to transform rehabilitation.
"The Prison Reform Trust's advice and information service has heard from prisoners at Oakwood for months, facing problems with access to the most basic necessities.
"As well as addressing concerns about safety and security at the jail, the regime and the impact of changes to the incentives and earned privileges scheme, it is important that the investigation into the disturbances at Oakwood sheds light on the feasibility of giant prisons run on ever tighter budgets.
"With the announcement today of planning permission for a 2,000-place prison in Wrexham, there is mounting concern over the Government's policy of building super-sized jails on the cheap and its impact on the safety and well-being of prisoners.
"Our research shows that nearly half of all prisoners will be held in prisons of 1,000 places or more under Government plans to transform the prison estate.
"This is despite evidence which shows that smaller prisons tend to be safer and more effective than larger establishments, holding people closer to home and with a higher ratio of prison staff to prisoners."