Boris Johnson and senior ministers could put more countries on the red list to avoid the possibility of a Christmas lockdown.
It comes as the new variant Omicron has been spreading across African countries with scientists warning about its severity.
Earlier in the week, the Government added South Africa, Botswana, Eswatini, Lesotho, Namibia and Zimbabwe to the list to avoid the variant coming to the country.
Senior Government scientists said the mutant variant was the “worst variant they have seen so far” – with vaccines expected to be at least a third less effective against it.
Experts warn the strain is behind an explosion of new cases in South Africa, with some regions seeing a six-fold rise in infections in a matter of days.
Flights from South Africa as well Namibia, Lesotho, Botswana, Eswatini and Zimbabwe were suspended from midday on Friday and all six countries were added to the red list, Health Secretary Sajid Javid said.
Malawi and Mozambique are expected to be added to Britain’s red list imminently and there is acceptance in Whitehall that further bans are likely.
A senior aviation source said there were “serious jitters” in all corners of the industry, telling The Times : “There is now a massive question mark over Christmas.
“It is clear the red list will expand and that will have a massive knock on.”
It comes as fears of a second Christmas lockdown grow, with Prof Adam Finn, from the Joint Committee on Vaccination and Immunisation, warning Brits to be “ready for the possibility of a change in the restrictions”.
Sajid Javid said the new variant identified in South Africa “may be more transmissible” than the Delta strain and added “the vaccines that we currently have may be less effective”.
Officials are also desperately trying to trace thousands who have arrived from South Africa in the past ten days.
Scientists said the new strain was unlikely to be in the UK, but with up to 700 people flying in a day, they could not rule it out.
Dr Susan Hopkins, chief medical adviser at the UK Health Security Agency, said it was “always possible” the variant had reached the UK.
Asked on BBC Radio 4’s Today Programme if it was in the UK, she said: “It’s always possible, we have no cases identified whatsoever yet.”
Currently called B.1.1.529, the bug has 32 mutations – twice as many as the delta variant.
As well as South Africa, it has also been found in Botswana and Hong Kong.
The World Health Organisation met on Friday to decide whether to classify the bug as an imminent threat.
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