Pubs and shops should be shut in order to reopen schools if a trade-off needs to be made because of a rise in coronavirus infections, the Children's Commissioner has told the Government.
Anne Longfield said that if lockdown restrictions needed to be reimposed because of local flare-ups in infection rates, schools must only be closed as a last resort to bring transmission down once all other options have been exhausted.
She criticised ministers for treating children as an "afterthought" during the first lockdown, adding that they must be put at the heart of planning for a second wave.
"That means schools must be the first to reopen and the last to close during any local lockdowns," she said. "If the choice has to be made in a local area about whether to keep pubs or schools open, then schools must always take priority."
It comes after England's chief medical officer warned that the country had "reached the limits" of how much could open up before infection rates started to increase.
Hinting at the idea that some businesses may have to close so that schools can reopen, Professor Chris Whitty said: "We are at the outer edge of what we can do, and therefore choices will need to be made. But people, I think, are very clear for example that schools are an absolute priority for the welfare of children."
Boris Johnson, the Prime Minister, has described reopening schools as a "national priority" but a Downing Street spokesman said on Tuesday night that the idea of closing pubs and restaurants to open schools was "hypothetical".
Government sources told The Telegraph that it is not as simple as closing pubs to open schools, because the aim of a local lockdown is to limit the movement of people in the community as much as possible and so transport to and from schools also needs to be taken into account.
The Children's Commissioner's warning comes amid fears that it will be impossible for the economy to fully reopen unless children are back at school full time.
The Government has promised to reopen schools in September, with all children attending a full timetable of classes every day, and fines will be reintroduced for parents who keep their children at home.
However, the Government published new regulations on regional lockdowns on Tuesday, which give councils the power to limit schools to certain year groups or close them down completely for all but the children of key workers and the most vulnerable.
Earlier this week, a Lancet study suggested that reopening schools without an improvement in test and trace could result in a second coronavirus wave more than twice the size of the first.
Researchers warned that just 50 per cent of contacts of positive cases are currently reached. The study found that if test and trace was more successful – so that 68 per cent of the contacts of positive cases were traced – the spread could be held in check.
Without improvements, the opening of schools and associated changes such as the return of parents to work could result in a second wave this winter that is two to 2.3 times the size of the first, they said.
Teaching unions are now demanding an "alternative strategy" to reopening schools in September, saying they need official guidance on how to proceed if there is a second lockdown.
Headteachers said that, while they support the ambition to get all children back into the classroom at the start of next academic year, a "Plan B" is urgently needed in case this is not possible.
In a development that threatens to open up a new row with the Government, unions have accused ministers of failing to draw up contingency plans for education if schools are unable to reopen.
"We remain concerned that the Government still lacks a 'Plan B' in the event that this does not prove possible because of infection rates, or if there is a second national shutdown," Julie McCulloch, the director of policy at the Association of School and College Leaders, said.
"Its guidance envisages only a scenario in which schools close on a local basis in response to infection spikes, and instructs them to have contingency plans in place."
The Children's Commissioner has published a new report which urges ministers to roll out regular testing of pupils and teachers, regardless of whether they have Covid-19 symptoms, to keep schools safe.
She also accused the Department for Education of lacking scientific expertise, which she said was stopping it from accurately assessing children's needs during the pandemic.
There is mounting concern about the long-term effects of school closures, particularly on children from the most deprived households.
The general secretary of the United Nations warned on Tuesday that the world faces a "generational catastrophe" due to school closures, adding that getting students safely back to the classroom must be "a top priority".
Sir Michael Wilshaw, a former chief inspector of schools in England, said it was an "absolute moral imperative" that teachers worked with students who have "fallen furthest behind".
Gavin Williamson, the Education Secretary, said: “Getting all children back into the classroom, full-time at the start of next month is a national priority, as this is the best place for them to be."