The chief inspector of prisons has said that four short-term immigration detention centres are still not up to standard despite previous critical reports.

In her latest findings, Anne Owers criticised "systemic deficits" in safety and "decency" at the centres at Luton and Stansted airports, Leeds and Portsmouth ferry port.

She said the centres were not fit for holding children or for overnight stays and called for minimum standards to be set by Home Office ministers for the Immigration and Nationality Directorate.

"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," Owers said.

"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."

Responding, Home Office minister Liam Byrne stressed that improvements had been made and that the use of the centres was not the norm

"I welcome Anne Owers' report into the four short-term holding facilities," he said. "I am pleased that changes and improvements were detected by the inspectors and that the efforts of staff were applauded.

"The report acknowledges that custody staff teams in all four facilities delivered good general standards of care, all of the facilities appeared to be well managed and that links to local immigration service teams were good. Anne Owers also welcomed the future planned involvement of the Independent Monitoring Boards for adding a necessary element of regular independent monitoring of short term holding facilities.

"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."