The UK is set to reimpose the wearing of mandatory face coverings in shops and on public transport, along with compulsory 10-day self-isolation for those who come into contact with positive cases of the new Covid-19 variant, Boris Johnson announced last night.

As the first two UK cases of Omicron were confirmed in Brentwood, Essex, and Nottingham, the British prime minister warned “we need to slow down the seeding of this variant” to “buy time” for scientists to establish whether it evades existing Covid-19 vaccines.

While twice insisting that “we are not going to stop people travelling”, Mr Johnson announced that all passengers arriving to the UK from abroad will now have to take a PCR test by the end of their second day after reaching Britain and self-isolate until they receive a negative result.

Flanked by Prof Chris Whitty, the UK’s chief medical officer, and Patrick Vallance, the chief scientific adviser, Mr Johnson also piled pressure on scientists on thec Joint Committee on Vaccination and Immunisation (JCVI).

He asked them to urgently consider rolling out booster jabs to all adults, as well as reducing the waiting period between second and third doses.

He said: “From today we’re going to boost the booster campaign.”

Prof Whitty revealed that the JCVI was “taking into account the fact this really changes the risk-benefit calculations for several of the decisions which they still have to take” and will “reassess the decisions they have taken”.

Extending the roll-out to all over-18-year-olds is, he said, the “most urgent decision they will have to take”, followed by the potential for a second dose for children aged 12-15, and for inoculating under-12s.

Last night UK officials were carrying out mass testing in affected areas to identify further cases, raising the prospect that many people could be asked to self-isolate soon after the new rules are imposed.

Genome sequencing was being carried out on positive cases to identify instances of omicron.

Sajid Javid, the UK Health Secretary, was due to announce further details of the new rules today, including setting out when they will come into effect.

Meanwhile, Germany announced last night that it had two confirmed cases of the Omicron Covid variant just hours after Britain declared its two cases.

Authorities in the southern state of Bavaria confirmed the two cases, after the travellers who arrived from South Africa four days ago personally sought out authorities to be tested after reading media reports about the new variant.

Two other foreign passengers who arrived in Bavaria on a flight from Cape Town on Friday had tested positive for coronavirus and authorities are investigating whether they were also infected with the new strain.

There is a third suspected case in the central region of Hesse.

The Bavarian health ministry requested of passengers who had arrived from South Africa on the same flight on November 24 to report immediately to their local health department.

Olaf Scholz, the German finance minister, who is expected to be sworn in as successor to Angela Merkel, the outgoing chancellor, early next month, stressed yesterday that his coalition would do “everything necessary” to fight “corona and Omicron”.

“There is nothing which can’t be considered,” he said.

Italy also confirmed its first case of the new variant in Milan, from a woman who had recently visited Mozambique.

Dutch health authorities were last night scrambling to see if the new Omicron variant had arrived in the country.

It comes after 61 passengers returning from South Africa tested positive for the virus.

Shutters are coming down across the world as Omicron, which is potentially more contagious and resistant to vaccinations, prompts fears of a major setback in the effort to end the pandemic.

Israel, which has one confirmed case, yesterday moved to prohibit tourism for two weeks and banned Israelis from travelling to countries on its red list.

The Czech Republic also identified its first suspected case of Omicron in a woman who recently travelled to Namibia.

Belgium, Hong Kong and Botswana have also recorded cases of the new variant.

One of the Hong Kong cases was believed to have become infected by someone who was staying in the opposite room while in a quarantine hotel.

While France had as of last night recorded no cases of the variant, it announced that any person who has been in contact with someone who has tested positive for the Omicron variant will be obliged to isolate even if they are fully vaccinated.

America’s Covid chief yesterday said that he “would not be surprised” if the new Omicron variant has already arrived in the US, but insisted that it has not yet been detected.

Anthony Fauci, chief medical adviser to President Joe Biden, said that although there was “not any reason to panic”, the new variant was to be taken seriously.

He said it also justified the travel ban against South Africa and seven neighbouring countries.

“It may not turn out (to be serious), but you want to be ahead of it.

"That’s why we’re doing what we’re doing,” Dr Fauci told NBC.

When asked if he thought it could already be in the country, Dr Fauci said: “I would not be surprised if it is.

“We have not detected it yet.

 "But when you have a virus that is showing this degree of transmissibility... it almost invariably is going to go all over,” he added. 

Telegraph Media Group Limited [2021]