At least 250 people who were detained at Manston asylum centre during a period when it was dangerously overcrowded and grappling with outbreaks of infectious diseases are suing the government for unlawful detention and other breaches of their rights.

They include a woman who had a miscarriage, a child whose age was recorded as five years older than he was, classifying him as an adult, and a teenager who was a victim of torture and trafficking.

The claims arise from a time when the Home Office’s site in Kent for processing people who had crossed the Channel on small boats was described by a senior union official as “a humanitarian crisis on British soil”.

The former independent chief inspector of borders and immigration, David Neal, said the poorly managed and insanitary conditions there were so bad he was rendered speechless.

Andy Baxter, the assistant general secretary of the Prison Officers’ Association, raised the alarm about conditions on the site in response to concerns from members of his union who worked there. After visiting, he described an unprecedented situation which more closely resembled a refugee camp in an unstable country than a Home Office temporary staging post for new arrivals to the UK in a tranquil corner of Kent.

At the time that Baxter said Manston was in crisis, marquees that were supposed to be used for a matter of hours before asylum seekers were moved to more permanent accommodation were used for more than a month in some cases. People slept on the dirty ground on pieces of sodden cardboard. There were outbreaks of diphtheria, a disease rarely seen in the UK thanks to vaccination, and scabies. One man died after contracting diphtheria while claims of guards assaulting asylum seekers were investigated by Kent police.

But it was only in the months after this bleak period – between June and November 2022 – that the full details of what happened there began to emerge.

Those bringing claims against the government include a 19-year-old from Sudan who was a victim of torture and trafficking, although his vulnerabilities were not recorded while he was detained at Manston for 33 days. He said he was often hungry and was only allowed one shower the whole time he was there. He was not given any change of clothes. He said that some of the officials he encountered at Manston told him to “go back to your country”.

Another claimant, a 17-year-old Kurdish boy from Iraq, was given a birth date five years older than his actual age, despite insisting he was a child. He was detained for 12 days.

A Syrian woman had a particularly difficult time. She arrived in the UK with her husband and their five young children, but when her husband complained to guards about the conditions at Manston he was removed from the site and placed in an immigration detention centre.

She did not know where he had been taken and feared he had been deported. She and the children spent 11 days in a freezing, filthy tent, and were only allowed to leave it to go to the toilet. When her children contracted a sickness bug that was circulating at Manston, she had nowhere to wash their vomit-stained clothes as there was a shortage of running water, so she tried to wash them using bottled water.

She herself vomited every morning and later discovered she was pregnant. She was unable to access medical care while in Manston, and when she was released and could seek treatment, it was discovered that the baby had died inside her. After she and her children were released from Manston, she was finally able to reunite with her husband but says that the impact of being detained in Manston continues to affect them all.

Emily Soothill of Deighton Pierce Glynn, who is representing some of those bringing legal action relating to their time at Manston, said: “We consider that our clients were falsely imprisoned and that the conditions in Manston were such that their human rights were breached. People seeking asylum are more vulnerable to physical and mental illness; they have the right to be treated with dignity and should not be detained in this way.”

Jed Pennington of Wilsons solicitors, representing others legally challenging their time in Manston, said: “The humanitarian crisis that unfolded at Manston in the autumn of 2022 is not what you would expect to see in a country with well-developed systems for accommodating refugees. Our clients want the truth about how it happened, who let it happen and how to prevent this from happening again.”