Stand Up to Racism, which has been in contact with asylum seekers who were moved from the barge, heard reports that they were notified about the bacteria at 4.45pm yesterday and then given a letter at 5pm.

The campaign group claimed there was no one to ask questions of when they were given the news and that they have not been tested for Legionnaires disease.

Heather, from Stand Up to Racism Dorset, said some of them claimed they had found out from "media reports".

She said: "One of them rang me and said 'I just drank the water. Should I be concerned? Should I give you my family's details in case something happens to me and you need to contact them'. I had to reassure them it was just caution, but it's really concerning that they found out from the press."

Stand Up To Racism have said they have spoken to migrants moved from the Bibby Stockholm and three have reported feeling unwell with a cough and headache. The men say they have been given blood tests.

The volunteer group says all the migrants who were onboard have been told they will see a doctor next week, Monday at the earliest.

It comes as Conservative ministers face calls to resign after Legionella bacteria, which can cause a serious type of lung infection known as Legionnaires' disease, was found in the water on the barge.

Heather also said the people on board who she has spoken to feel "completely unsettled" and "feel like they're not being valued as humans". Stand Up to Racism said coaches arrived at 7pm and they were taken to a hotel "several hours away" from the barge.

The group claimed the rooms they were given did not have fresh linen until this morning, adding that the men are "very tired and re-traumatised by this experience. They don't feel safe".

Conservative backbenchers have accused the Home Office of "incompetence" after the 39 people who had boarded the vessel were transferred to alternative accommodation on Friday evening.

Shadow immigration minister Stephen Kinnock wrote to the opposition on Saturday asking what the department knew about the risk of the bacteria being present before moving migrants onto the barge.

The department said all those on board had been disembarked as a "precautionary measure" after samples from the water system showed levels of Legionella requiring further investigation.

The Home Office said no migrants have fallen sick or developed Legionnaires' disease and were all being provided with "appropriate advice and support".

Home Secretary Suella Braverman is now under growing pressure to scrap plans to house asylum seekers on barges altogether, following a significant setback to a policy that has been beset with controversy and delay from the very start.

Campaigners from No To The Barge have also said immigration minister Robert Jenrick should stand down from his government position with "immediate effect" after promising just days ago that the barge was safe.

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The Home Office insisted disembarking those on board was a "precautionary measure" while further tests are carried out - but questions remain about who knew what and when.

Sky News understands routine testing of the water supply was initially carried out on Tuesday 25 July, but the results did not come back until Monday 7 August - the same day asylum seekers began to board the Bibby Stockholm, which is docked in Portland Port.

However, the Home Office was not made aware of the results until two days later on Wednesday 9 August. Six people boarded the vessel a day later but were later removed on the advice of the UK Health Security Agency, with a decision taken on Friday to remove everyone.