Suella Braverman is under pressure to abandon plans to house asylum seekers on a barge after 39 people had to be removed from the vessel after the discovery of potentially deadly bacteria in the water system. Ministers said they were concerned contractors knew there were traces of legionella bacteria on the Bibby Stockholm on Monday, when the first asylum seekers boarded the vessel in Portland, Dorset. Officials have insisted the Home Office was not told about the detection until Wednesday when further tests were ordered. So far none of the people on the barge have tested positive for the disease, but it can take up to 16 days for symptoms to emerge. A leaked Home Office letter seen by the Guardian shows asylum seekers have been told they will be tested if they show a range of symptoms including dry coughs, confusion and diarrhoea. The developments come at the end of Rishi Sunak’s “small boats week” which was supposed to announce new hardline policies to reduce the number of asylum seekers attempting to enter the UK. On Monday, the government dropped plans to send migrants 4,000 miles away to Ascension Island just hours after it was announced. The Conservative deputy chair, Lee Anderson, provoked outrage when he told asylum seekers to “fuck off back to France”, before later admitting the government had “failed” to tackle illegal immigration. A £400,000 Home Office drone used to monitor boats in the Channel crashed into the sea. And on Thursday, 755 asylum seekers were recorded crossing the Channel, the highest number in a single day. Home Office sources said tests for legionella were carried out on 25 July. Lower level traces were identified on Monday as the first asylum seekers were taken on to the barge. It is understood a contractor, Landry and Kling, was told about the concerns. The Home Office first learned about the early traces on Wednesday, resulting in further tests on Thursday, sources said. The Home Office still sent another six people on to the barge on Thursday, sources confirmed, but after taking advice from the UK Health Security Agency, these people were taken off that evening, and everyone else was removed on Friday. People can get lung infections, such as legionnaires’ disease or Pontiac fever, if they breathe in small droplets of water in the air that contain the bacteria. Carralyn Parkes, the mayor of Portland, said she was astounded that a basic check carried out by councils every day appeared not to have been done in a timely manner. “I am shocked and horrified by the incompetence of this government. We were told that all of these checks had been done,” she said. “Portland town council has to do legionnaires’ disease checks on public lavatories and we do that competently. And yet the Home Office, which is supposed to be helping to run the country, has failed to complete basic checks.” The shadow immigration minister, Stephen Kinnock, said it was “extraordinary” that it appeared proper checks had not taken place before people were moved onboard. “It’s absolutely right that the barge has to be evacuated, but what a complete and utter shambles. This is a catalogue of catastrophe, and government ministers should hang their heads in shame,” he told Sky News. The Home Office said environmental samples from the water system on the Bibby Stockholm had shown levels of legionella bacteria that required further investigation. On Friday night, a spokesperson said: “The health and welfare of asylum seekers remains of the utmost priority. All asylum seekers accommodated on the Bibby Stockholm have now been disembarked as a precaution and moved to alternative accommodation. “The Home Office and our contractors are following all protocol and advice from Dorset council’s environmental health team, UK Health Security Agency and Dorset NHS who we are working closely with.” Earlier, the Home Office said the samples related only to the water system on the barge and there was “no direct risk indication” for the rest of Portland. They were not related to fresh water entering the vessel. Several people refused to board the vessel last week amid warnings from the Home Office that they would face having government support removed if they did not. On Wednesday, Robert Jenrick described the barge as “perfectly decent accommodation”, despite earlier warnings from the Fire Brigades Union that the vessel was a “death trap”. The FBU’s assistant general secretary, Ben Selby, said the govrnment had ignored its concerns over health and safety. “The Fire Brigades Union warned the home secretary that forcibly holding migrants on this barge was a huge health and safety risk. “We wrote to Suella Braverman more than a week ago to demand a meeting to discuss these issues. We have had no response to that letter,” he said. A Dorset council spokesperson said no one presented with symptoms of legionnaires’ disease, and there was no health risk to the wider Portland community. It is understood the Home Office is managing the search for alternative accommodation for the asylum seekers. Nicola David, of the NGO One Life to Live, which has conducted research which claims the barge is not a safe place to accommodate asylum seekers, said that the government has urgent questions to answer and ministers are ultimately responsible. David said: “There are too many private companies involved in the barge deal and they are not experienced in providing accommodation for asylum seekers. Tragically, today the asylum seekers were the last to know about what was going on. This was Suella Braverman’s baby but when she should be answering questions about what went wrong she is nowhere to be seen.” A spokesperson for the charity Freedom from Torture said: “The presence of life-threatening bacteria onboard the Bibby Stockholm is just another shocking revelation that we’ve seen unfold over the past few weeks. This government’s punitive policies and deliberate neglect of the asylum system is not just cruel, it’s dangerous. “This government urgently needs to stop forcing refugees into unsafe and undignified accommodation, and instead focus their efforts on rebuilding a compassionate and efficient system that protects people like me who have fled torture and persecution.” A spokesperson for the group Stand Up to Racism Dorset said activists were heading to the port to protest about the Home Office’s treatment of asylum seekers. “This is yet another example of the Home Office’s incompetence and inhumanity.” This article was amended on 11 August 2023. Portland Port is in Dorset, not Devon as an earlier version stated.