Health secretary Matt Hancock said anyone arriving from South Africa in the past fortnight or anyone in close contact must immediately go into quarantine.
He said the third variant had been discovered in people close to those who had travelled to South Africa “in the past few weeks”.
The new variant was highly concerning because it was more transmissible than others, he said. Hancock said immediate restrictions would be placed on travellers from South Africa.
“Anyone in the UK that has been in South Africa in the past two weeks or is in close contact must quarantine immediately. They must restrict all close contact with anyone whatsoever.”
Hancock also said Covid cases across the UK had risen 57% in the past week.
