Schools will close except for looking after the children of keyworkers and vulnerable children, Prime Minister Boris Johnson has said.
This academic year's exams will not go ahead in England and Wales; decisions are due to be made in Scotland and Northern Ireland.
It came as UK deaths reached 104 after a further 33 people died.
Thirty-two were in England and one in Scotland.
Confirmed cases in the UK rose to 2,626 on Wednesday, from 1,950 on Tuesday. There have been 56,221 tests carried out in the UK for Covid-19, of which 53,595 were confirmed negative.
The government says it plans to more than double the number of tests being carried out in England to 25,000 a day. SHARE THIS NEWS USING ANY OF THE BUTTON BELOW PLACE YOUR TEXT ADVERT BELOW ⬇⬇⬇