The decision to significantly tighten the rules, one the Prime Minister has resisted for months since the back-up plan was announced in September, applies to people in England only.

There are four elements to it: new work from home guidance, the introduction of Covid passports, an expansion of face mask mandates and changes to isolation rules.

The work from home guidance will kick in on Monday, with Mr Johnson saying: “Go to work if you must, but work from home if you can.”

Christmas parties allowed – but with ‘due caution’

However, when asked what his message was on Christmas parties and nativity plays, Mr Johnson said they should not be cancelled.

“We think it’s OK currently, on what we can see, to keep going with Christmas parties, but obviously everybody should exercise due caution.”

The message repeats a position he took last week, but means people are now being urged to work from home if possible but also not to cancel Christmas parties, which critics said was confusing.

John Redwood, the Tory MP and former Welsh secretary, criticised the decision to both urge people to work from home next week but also not scrap Christmas parties.

He said: “It doesn’t make any sense. It was clearly contradictory. The Government should think again.”

Andrew Bridgen, another Tory MP, said: “For a government which claims to follow the science, I think they’ve lost their marbles. The restrictions are incoherent and irrational.”

The Prime Minister did urge people to take lateral flow tests, which are still available free from pharmacies, before attending such parties.

Covid passports return

Covid passports will come into force in England next week. A change in the original plan has been adopted, with people able to show proof of a negative test as well as two doses of a Covid vaccine.

They will be required for entry into nightclubs, most indoor venues with more than 500 people, unseated outdoor venues with more than 4,000 people and any venue with more than 10,000 people.

The ability for venues to successfully apply the new rules remains an open question, with implementation of a similar policy in Scotland causing problems that resulted in a loosening of the requirements.

A third area of change is face masks, which had just been legally required on public transport and in shops but will now apply to most public spaces.

Mr Johnson said places where “eating, drinking, exercising or singing” takes place would be exempt, given that wearing face masks there was not practical.

Face masks in classrooms are not expected to be required, according to a Number 10 source.

Moves to stave off another ‘pingdemic’

A move to counter concerns of a new “pingdemic” were also announced, with daily tests instead of a 10-day isolation needed if people come into contact with someone who has the omicron variant.

It should mean that those who test negative will not have to self-isolate, though it remained unclear exactly when the change would come into effect.

A heated backlash to the Covid rules, fuelled by allegations of Number 10 rule-breaking at Christmas parties, was already building among backbench Tory MPs on Wednesday night.