Boris Johnson has toughened coronavirus measures in England amid concern over the increasing spread of the Omicron variant.

Speaking at a Downing Street news conference on Wednesday evening, the prime minister announced the measures in the government’s “Plan B” for dealing with COVID-19 this winter.

Mr Johnson said it had become “increasingly clear” that Omicron, first detected in South Africa, is “growing much faster” than the previous Delta variant and was “spreading rapidly all around the world”.

He added it was “the proportionate and the responsible thing” to introduce stronger COVID restrictions.

The new COVID measures in England announced by the prime minister included:

• The reintroduction of the work from home order, for those who can, from Monday
• The extension of mandatory face mask wearing to “most public indoor venues”, including theatres and cinemas. However, there will be exemptions “where it is not practical”, such as when eating, drinking, exercising or singing
• The NHS COVID pass, commonly referred to as a vaccine passport, will be made mandatory in a week’s time for nightclubs and large events. People can show either proof of two vaccine doses or a negative lateral flow test result.

Earlier on Wednesday, it was revealed that another 131 cases of Omicron – which is feared to be more transmissible than the Delta variant – had been recorded across the UK, taking the total to 568.

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It marks the second day in a row that more than 100 cases of the new variant have been reported.

But Mr Johnson warned the “true number” of Omicron cases was “certain to be much higher”.

“Most worryingly, there is evidence that the doubling time of Omicron in the UK could currently be between two and three days,” he added.

“And while there are some limits to what we can learn from South Africa – because of the different rates of vaccination and different rates of previous infection – we are seeing growth in cases here in the UK that mirrors the rapid increases previously seen in South Africa.

“South Africa is also seeing hospitalisations roughly doubling in a week, meaning that we can’t yet assume Omicron is less severe than previous variants.”

The prime minister acknowledged the “remorseless logic of exponential growth” of Omicron in the UK could lead to “a big rise in hospitalisations and therefore, sadly, in deaths”.

In total, the UK has recorded 51,342 new COVID cases in the last 24 hours and a further 161 people have died within 28 days of testing positive for coronavirus.

Mr Johnson made the announcement of fresh COVID measures as he deals with a furious row over an alleged Christmas party in 10 Downing Street last December, when strict coronavirus rules were in place.

Amid the scandal, the prime minister has faced the charge he is implementing stronger COVID measures as a “diversionary tactic”.

In a document published in September, the government’s “Plan B” for dealing with winter pressures in the NHS stated that contingency measures to deal with COVID-19 would include a strengthening of government messaging, the possible introduction of COVID vaccine passports for some events, mandatory face mask wearing, and a return to work from home guidance.

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Mr Johnson had already reintroduced mandatory face mask wearing on public transport and in shops, as well as other settings in England, following the discovery of the Omicron variant last month.

He has also recently toughened travel restrictions and put a number of African countries on the travel red list.