Four immigration detention centres in England have failed to provide "basic standards of decency and safety", the Chief Inspector of Prisons has said.
Inspectors will be visiting the sites again to check on improvements
Anne Owers reported "systemic deficits" at Luton and Stansted airports, the reporting centre at Waterside Court in Leeds, and Portsmouth ferry port.
The centres, run by private contractor G4S, were not fit for holding children or for overnight stays, she said.
G4S said they had already taken steps to address many of the issues raised.
The report found that, although improvements were being made, minimum standards had yet to be set.
At Leeds, detainees with special needs, including those at risk of self-harm, were routinely held in police cells.
The Portsmouth facility was described as "inadequate, cramped and potentially unsafe".
Ms Owers said: "We have detected changes and improvements since we began these routine inspections, and we applaud the efforts of staff to mitigate the inadequacies of some of the facilities.
"The Immigration and Nationality Directorate, with the contractors, should be setting and enforcing minimum standards that reflect the actual usage of these facilities.
"We hope to see our repeated recommendations reflected in revised operating standards that ensure basic standards of decency and safety."
The inspectors found that staff were concerned about the suitability and safety of escort vehicles provided by G4S.
But G4S welcomed the report and said it was confident of the quality of services it provided.
Director Gavin Windsor said: "We have already, in conjunction with the Immigration and Nationality Directorate, taken various steps to address many of the issues raised in the reports and will continue to work with the IND in taking any further action required."
In a separate report, Ms Owers examined conditions experienced by immigration detainees while being escorted from place to place by a private contractor.
Detainees interviewed at Heathrow airport by inspectors complained about the lengths of journeys and the inadequate number of toilet breaks.
One man said he had been forced to sit next to a man who was sick during a five-hour journey, with staff only making cursory efforts to clean up the mess.
Home Office minister Liam Byrne said: "I take very seriously the recommendations in both of these reports and an action plan responding in detail to each of the recommendations is currently being drawn up.
"It is important to understand these facilities are intended to accommodate people for very brief periods.
"Short-term detention is only used when absolutely necessary prior to removal or when further investigations are made on individuals arriving in the UK.
"Detention is an essential part of an effective immigration system, but it is critical that it is done with humanity and dignity."
Leeds No Borders, a campaign group which opposes all immigration controls, is to stage a demonstration on Thursday outside the city's Waterside Court centre "to mark our opposition to the inhumane treatment there".