British schools close indefinitely on Friday as part of tougher government measures to stem the coronavirus pandemic, following similar shutdowns in Europe and across the world.
Prime Minister Boris Johnson had resisted the move, fearing its impact on the workforce, but changed course as the COVID-19 outbreak worsened across Britain.
The number of confirmed infections inside the country doubled between Monday and Thursday to 3,269 cases, while the death toll nearly trebled to 144 deaths in the same period.
The government released details of which essential frontline workers will still be able to send their children to schools for care.
They include those of health and social care staff, educators and child carers, key public service workers such as police as well as food and distribution sector employees.
"The school closures are there to slow the spread," Health Secretary Matt Hancock told Sky News television, noting the exemptions should result in fewer than one in five children going to school.
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"We're going to make sure that they don't reduce the capacity of the NHS as well," he added, referring to Britain's state-run national health service.
But the closures have sparked concern about the impact on pupils whose end-of-year exams have been cancelled. Further guidance about grading is expected.
Meanwhile Hancock said the sector's regulator was writing Friday to 65,000 doctors and nurses who had recently retired, "to say please come back into practice as soon as you possibly can".
He insisted Britain's response had been proportionate to the pandemic's spread.
"We're further behind the growth of this virus than in Italy... the growth here in the early days was slower than in the rest of Europe.