Ministers have received an official warning that the UK’s largest accommodation site for asylum seekers is at immediate risk of descending into criminality, arson and assaults on staff, letters released under the Freedom of Information Act show. The immigration watchdog, David Neal, has written to the home office ministers James Cleverly and Tom Pursglove saying “hopelessness caused by boredom” among hundreds of young men at the Wethersfield airbase will “inevitably” lead to harm. The warnings follow two visits in December and February to the remote site in Cleverly’s Essex constituency by Neal, the independent chief inspector of borders and immigration, after violent clashes between groups of migrants. Officials have planned to increase the number of asylum seekers from 565 to 800 held on the Essex airbase, which is ringed by security fences and monitored round the clock by on-site security guards and CCTV. There are no pavements on the roads around the site and no public transport. In a letter to Cleverly in December, Neal warned that the conditions in which asylum seekers were being held – with a lack of reliable wifi and without purposeful activity – would lead to their worsening mental health and a breakdown in relationships with staff. “I am not confident that the Home Office has the right people or the right plans or that it is moving at sufficient speed to keep service users safe. Unless this is addressed as a matter of urgency I predict the frustration of service users will lead to increased criminality, including arson,” he said. Neal visited the barracks in August and again on 19 December, and found there had been an increase in violent incidents which had led to a rise in the numbers of Home Office staff on the site, he wrote. “The staff move is a positive step but they have neither the experience of residential settings nor the training to deliver solutions and address what could become a serious issue over the coming weeks,” he wrote. The home secretary was warned by Neal that some of the factors that led to disorder and attacks on local residents by Libyan cadets at Bassingbourn barracks, near Cambridge, in 2015 could be seen at Wethersfield. “Isolated assaults on staff led to increased security and anxiety amongst staff which led to increased violence. I fear that some of the factors experienced at Bassingbourn are present at Wethersfield now,” he wrote. The Home Office should seek advice from HM Prison and Probation service on how to occupy “hundreds of men in an isolated camp”, Neal wrote. Neal met Cleverly on 25 January and discussed Wethersfield, officials confirmed. In a second letter, sent to Pursglove, Neal wrote that he had visited Wethersfield on 8 February and had seen “no improvement” at the remote Essex site. “Nothing substantive has been delivered to relieve and to mitigate the risks resulting from the tensions that will inevitably arise when a sizeable population of men is being accommodated in a remote location with very limited information on what the future might hold for them and with very little to do,” he wrote. “I spoke to a number of men and it was clear there was an overwhelming feeling of hopelessness caused by boredom which inevitably in my experience leads to violence.” In the letter, Neal wrote that ministers were due to decide on 12 February whether to increase the number of asylum seekers held at the site to 800. “I am concerned that this expansion in numbers would significantly increase the risk of a serious incident impacting the safety and wellbeing of Home Office staff, contractors, and service users on site,” he wrote. Steve Smith, the CEO of the refugee charity Care4Calais, which has launched a legal challenge claiming that asylum seekers are unlawfully segregated from the local population, said: “The chief inspector’s letters are absolutely damning. He has directly warned the home secretary and his immigration ministers that the operation of the Wethersfield site risks the safety of residents at the camp, and yet no action has been taken in two months.” A Home Office spokesperson said the department disagrees with Neal’s assessment. “We disagree with this assessment. We take the safety and welfare of asylum seekers at Wethersfield extremely seriously and we will increase occupancy of the site while prioritising welfare and integration. “Wethersfield is designed to provide adequate and functional accommodation for male asylum seekers and is designed to be as self-sufficient as possible, helping to minimise the impact on local communities and services. We do however provide communal spaces, faith and worship facilities and a large gymnasium to allow for recreational and sporting activity. “All residents have access to medical support, including mental health support, and a 24/7 helpline provided by Migrant Help is available to raise any concerns.”