The decision to force air passengers into quarantine when they arrive in the UK “doesn’t make sense” at this stage of the coronavirus pandemic, a senior government adviser has told the Guardian, piling pressure on ministers to explain the scientific basis for their border policies. Air passengers are facing mandatory quarantine on arrival to avert a new wave of infections as lockdown measures are eased. Boris Johnson told the nation on Sunday: “To prevent reinfection from abroad, I am serving notice that it will soon be the time – with transmission significantly lower – to impose quarantine on people coming into this country by air.” The measures, set to be introduced at the end of the month, will reportedly see air passengers asked to provide an address where they will self-isolate for 14 days, with spot checks and fines for breaches - but will not apply to sea or rail arrivals. The source told the Guardian the plans would only reduce risk if the UK had lower rates of infection than the countries from which passengers were arriving, which is no longer the case for most nations in the European Union. Speaking anonymously, the government adviser said: “There was really no scientific advice to inform the latest announcement. It also doesn’t really make sense for countries which have lower per capita current Covid case numbers than us; for example, most of the EU. “That sort of policy only reduces risk in the situation where we have very low case numbers and origin countries have much higher numbers.” Britain’s aviation and tourism industries warned that the quarantine plan risks worsening the economic impact of Covid-19. A letter signed by the chief executives of easyJet, Heathrow and Gatwick voiced “collective and serious concern and frustration”, adding: “An open-ended quarantine, with no set end date, will make an already critical situation for UK aviation, and all the businesses we support, even worse.” There has been mounting scrutiny of UK border controls in the run-up to the crisis. It emerged that 18.1m people arrived in the UK by land, sea and air between 1 January and 23 March and only 273 were formally quarantined. Until 13 March the government advised incoming passengers from specific hotspot countries, including Italy, Iran and parts of China, to self-isolate, but this was dropped – “inexplicably”, according to Yvette Cooper, the chair of the home affairs select committee. Since then, the government has relied on posters and leaflets to keep new arrivals informed. In April, with flight routes cut and a call to end all but essential travel, at least 95,000 people entered the UK. Asked if an enforced quarantine policy would have had more impact before the lockdown, the senior adviser said: “Everyone was unaware of the extent to which the virus had been seeded into Spain and Italy until those outbreaks started resulting in large numbers of hospital cases. At which point Spain and Italy were added to the list of countries for which traveller surveillance was in force. “However, we now know that a lot of infection was being seeded into London at about the same time as it was being seeded in Italy and Spain. It is also clear now that the border surveillance in place – looking for cases in travellers – missed most cases. “Compulsory quarantine of all travellers might have had a greater impact, but it’s not something we’ve looked at in detail. But without doubt, introducing lockdown earlier would have had the biggest impact on total deaths.” The Scientific Advisory Group for Emergencies (Sage) discussed the forthcoming measures at a meeting on 7 May but the advice it issued is yet to be published. A spokesperson said it would be published in “coming weeks”. Prof Gary McLean, a professor in molecular immunology at London Metropolitan University, backed the adviser’s view. He said the plans for new border measures “don’t make logical sense”, adding: “In all reality they should’ve done this two months ago, not now.” McLean said the continued community transmission of Covid-19 in the UK, with new official figures suggesting 10,000 new cases a day, meant that imposing a quarantine on arrivals would be unlikely to make much difference to the trajectory of the epidemic. “If our internal community numbers were to drop down to very low by the end of this month it may be worthwhile, but while we’re seeing community transmission here already I don’t know how it’s going to make any difference,” he said. The decision to impose restrictions only on those arriving by air also makes no sense, he said. “There’s nothing to stop someone from New York flying to Paris and taking the Eurostar to London,” he said. “We started [restrictions] late and we’re finishing early. It’s really crazy. It’s driven by political decisions and economic problems they want to fix. This bolt-on of 14-day quarantine for air travel is just bizarre.” The government is yet to publish the scientific advice from Sage on controls at the border, despite repeated requests from MPs. At a commons select committee on Wednesday, John Aston, the Home Office chief scientific adviser, who attends meetings of Sage, repeatedly failed to provide an estimated proportion or number of people who had arrived in the UK with Covid-19. He said that a more “robust” assessment was the ratio of imported cases to domestic cases. This model, formulated by Sage, estimates 0.5% of all cases on any given day were imported from overseas. A government spokesperson said: “As the prime minister said, we will soon be introducing measures that will mean those arriving in the UK from overseas will be required to self-isolate to help to keep transmission levels low and prevent re-infection from abroad and a second wave of cases that overwhelms the NHS. “We have been clear that people should not travel abroad except for essential journeys, and the vast majority of people have complied with our approach which is, and has always been, driven by the latest scientific and medical advice. Passenger arrivals in the UK at the end of April were down by 99%.”