Migrants who crossed the Channel to Britain from northern France are being held in substandard conditions despite government promises to improve accommodation, inspectors said Thursday.

The findings by the Inspectorate of Prisons and independent volunteer monitoring groups came after visits to migrant detention facilities in the last three months.

They found women who said they had been raped by smuggling gangs were "not adequately supported" and lone children were being held with unrelated adults.

A previous inspection in September 2020 found the same facilities were "badly equipped to meet their purpose," the chief inspector of prisons, Charlie Taylor, said.

The Home Office had then assured "rapid action" to improve conditions.

But he added: "Despite some limited progress, detainees, including large numbers of unaccompanied children, continued to experience very poor treatment and conditions."

Taylor said it was not immediately clear why government assurances had not been followed through, although inspectors were told of difficulties in coordination.

Anne Owers, a predecessor of Taylor as chief inspector of prisons who now chairs the Dover and Heathrow Independent Monitoring Boards (IMB), said "urgent action" was required.

Britain has this year faced an unprecedented number of arrivals of migrants using small boats to cross the Channel.

The situation has become a political headache for Britain, which vowed to "take back control " of its borders after leaving the European Union – and strained ties with France.

U.K. Prime Minister Boris Johnson outraged France by urging them to take back migrants who have crossed the busy shipping lane and is seeking to tighten immigration laws.

Last month 27 men, women and children drowned when their boat sank in November.

'Inappropriate'

The inspectors said families with young children were among those who have had to spend more than 24 hours in tents after arriving to be processed at Tug Haven, near Dover.

They highlighted "inadequate follow-up care" for two women who said they had been raped, and another who said she had been "sold into domestic servitude."

Migrants were held in "increasingly cold conditions," including on double-decker buses used to transport migrants and which were sometimes used for sleeping, they added.

They also raised concerns about injuries sustained by migrants on the crossing, including fuel burns, cuts and bruises, which went unnoticed on arrival and at processing.

On Wednesday, a local parliamentarian in Kent, southeast England, said a military base chosen by the Home Office to process migrants by January 2022 was "unworkable and unacceptable."

Officials have proposed using part of the Ministry of Defense site at Manston to hold people for up to five days while security and asylum checks are carried out. But North Thanet member of Parliament Roger Gale said the site was "inappropriate."

Other parliamentarians have said using military style accommodation was unsuitable and potentially traumatic for migrants, many of whom had fled war and violence.