Botswana, Eswatini, Lesotho, Namibia, South Africa and Zimbabwe have all been placed on the UK red list.
Flights from these countries will be suspended from 12pm on Friday until 4am on Sunday.
“That gives us a bit of time for the scientists to work on sequencing the genome, which involves growing cultures – it takes several weeks to do – so we can find out how significant a concern this particular variant is.
“It is a safety-first approach.
“We have done that before with things like the mink variant from Denmark and we were then able to relax it reasonably quickly.”
He later told the BBC: “I hope that’s what this is, a pause rather than going backwards, but we can’t take risks when we see a variant which could well defeat the vaccine, or at least that’s the concern and we need just a bit of time to check that out.
“The concern about this particular variant is that it is spreading very, very fast, its rate of growth has been very quick, we think the issue is probably (starting) from now, so we’re asking people to quarantine, self-isolate when they get home.”
The UKHSC has said the new B.1.1.529 variant identified in South Africa is the “worst one we’ve seen so far”.