The Royal Navy is threatening to “walk away” from Boris Johnson and Priti Patel’s plan to stem the number of boats carrying asylum seekers across the Channel as official data shows how spectacularly the policy has backfired. Defence chiefs are said to be fed up with trying to enact the prime minister and home secretary’s rapidly imploding plan of using the military to control small boats in the Channel. Ministry of Defence data shows crossings have close to doubled since the military was given “primacy” over the issue from mid-April compared with the first three months of this year. Patel and Johnson were warned that deploying the Royal Navy would be likely to increase the number of crossings but ignored expert advice because, according to internal sources, they wanted to appear tough. One former defence minister told the Observer that their miscalculation had guaranteed the navy was effectively providing an “efficient taxi service” for asylum seekers. Meanwhile, senior Home Office sources have admitted the UK could receive up to 60,000 people by small boat this year – double last year’s record – with another 20,000 arriving by different routes, undermining the credibility of Patel, who has made reducing crossings her priority. Patel will be grilled by the home affairs select committee this Wednesday on Channel crossings, the lack of safe, legal passage to the UK and her Rwanda asylum plan. The government has spent significant sums trying to remove asylum seekers to east Africa, but has yet to deport a single person. Defence chiefs hope Johnson’s resignation is an opportunity to scrap the Channel initiative as it also ties up resources at a time of escalating international security threats. Tobias Ellwood, Conservative chair of the influential defence committee, which has completed a damning inquiry into the use of the military in the Channel, said: “I know the MoD really wants to walk away from this, wants this to conclude. There’ll be less political pressure now. The prime minister is going.” The former soldier added: “From my personal perspective, I can say this is a complete waste of naval time. The navy is already overstretched.” John Spellar, the Labour vice-chair of the defence committee and a former defence minister, said the scheme had effectively reduced the navy to a “taxi service”. Spellar added: “As is now demonstrated, it is not achieving any significant improvement in the situation, but it’s embroiling the military in a task for which they are not suited and which is potentially reputationally damaging.” Their committee has heard evidence from naval commanders that the use of navy assets would, far from being a deterrent, make the crossing safer and therefore more attractive to small boats. This Tuesday, the armed forces minister James Heappey will be questioned by the committee over the operation’s predicted and actual lack of operational effectiveness. His appearance comes after ministers and officials from the Ministry of Defence and the Home Office refused to give evidence to the defence committee’s inquiry. When the Home Office and MoD were asked by the Observer to explain the legal basis for the military’s involvement in the Channel under so-called Operation Isotrope, neither would answer. It is also understood that the national security council, the main forum for collective discussion of the government’s objectives for national security, was not consulted before Isotrope was announced. MoD data shows a clear increase in migrants crossing in small boats. In May, 2,871 migrants were apprehended crossing the Channel by small boat compared with 1,627 in May 2021, a 75% increase. Similarly, during the first three months of 2022, 4,540 people were detected arriving by small boats compared with 7,432 during the last half of April, May and June after the MoD took over. Enver Solomon, chief executive of the Refugee Council, said the use of the navy had been proved to be futile. He said: “It is also expensive and demonstrates how the government is obsessed with control over both compassion and competence. “Prime ministers since Churchill have always given people fleeing persecution and bloodshed a fair hearing on UK soil. Using the military to repel them and seeking to expel them to Rwanda is a nasty and brutish response.” The MoD said: “As part of the government’s efforts to tackle illegal migration, the Ministry of Defence took primacy for the operational response to small-boat migration in the Channel in April. “The armed forces are supplementing Border Force assets, expertise and experience and providing operational oversight and coordination of maritime operations. This arrangement is likely to remain in place until early 2023.” A Home Office spokesperson said: “The government is united in tackling illegal migration and saving lives, to suggest otherwise is misleading and incorrect. “No one should be putting their lives at risk in the hands of people-smuggling gangs by getting into a small boat to cross the dangerous Channel. “The government’s new plan for immigration is the most comprehensive reform of the asylum system and will ensure we support those in genuine need while preventing abuse and deterring illegal entry to the UK.”