Fears are being expressed that Christmas will be affected by the arrival of the omicron variant of the Covid virus from southern Africa.

The British government acted quickly in order to buy time but not quickly enough. Two cases have been detected — one in Brentwood, Essex, and the other in Nottingham. Both were linked to travel in southern Africa.

The Sunday Times page one headline summed up the possibility that things will only get worse: “Christmas plans thrown into doubt as new Covid variant arrives in UK.”

Until Thursday few had heard of the word “omicron”, the 15th letter of the Greek alphabet assigned to the new variant.

On Friday night, Prime Minister Boris Johnson held a hastily convened conference at 10 Downing Street to announce that wearing face coverings would be compulsory on public transport and in shops in England from Tuesday.

On Sunday, health secretary Sajid Javid emphasised the new rules, saying the government had acted “swiftly” and “in a proportionate way”.

Significantly, neither the Prime Minister nor Javid were able to give a guarantee that Christmas will not be “cancelled”.

“I think it’s fair to say that the nature of this pandemic is it would be irresponsible to make guarantees,” said Javid. “As for Christmas, I think people should continue with their plans as normal for Christmas, I think it’s going to be a great Christmas.”

Boris refused to rule out a Christmas lockdown when pressed by reporters, warning that omicron “diverges quite significantly” from other Covid variants and that it will “reduce the protections of our vaccines over time”.

He was only willing to provide a lukewarm commitment that the festive season will be “better” than last year’s.

Boris said: “Our scientists are learning more hour by hour, and it does appear that omicron spreads very rapidly, and can be spread between people who are double vaccinated.”

Boris was flanked by two heavyweights: Prof. Chris Whitty and Patrick Vallance, the UK government’s chief medical adviser and the chief scientific officer, respectively.

Whitty said there was “a reasonable chance that at least there will be some degree of vaccine escape with this variant”, the first admission of this kind from a UK health official.

Vallance warned that the UK may need to “face up” to the possibility of further restrictions if the omicron variant is very transmissible.

Under the government’s plans, “everyone entering the UK (other than those coming from the Common Travel Area that covers the Channel Islands and Ireland) will have to take a PCR test by the end of the second day after their arrival and self-isolate until they receive a negative result.

“All contacts of suspected omicron cases must self-isolate, regardless of whether or not they are fully vaccinated.

“Face coverings will be made compulsory in shops and on public transport — but pubs and restaurants are exempt.”

One change has already been implemented. Ten countries — South Africa, Namibia, Zimbabwe, Botswana, Lesotho, Eswatini, Angola, Mozambique, Malawi and Zambia — are now on the UK’s travel red list. Until further notice, any British or Irish residents arriving in the UK after recently visiting any of these countries will have to quarantine in an approved hotel for 10 days.

Residents from the countries themselves will not be allowed into the UK until the red list status changes.