The omicron spread in London is now so serious, accounting for 80 per cent of new infections, that mayor Sadiq Khan has declared a “major incident” in the city, insisting further restrictions were now necessary to prevent hospitals being overwhelmed.

The mayor’s announcement comes as the number of Covid-19 cases in London has rapidly increased, with 65,525 new confirmed cases in the past seven days, and 26,418 cases reported in the last 24-hour period alone — the highest number since the start of the pandemic. In the last week, the number of Covid-19 patients in London hospitals has gone up 29 per cent.

Sadiq said: “The surge in cases of the omicron variant across our capital is hugely concerning, so we are once again declaring a major incident because of the threat of Covid-19 to our city.”

He added: “It’s right that London’s key agencies work closely together to minimise the impact on our city, including helping to protect the vital vaccination programme. I urge all Londoners to book their appointment or to go to one of the many walk-in centres across the capital as soon as you can.”

On Sunday, he appeared on the Andrew Marr Show and said new Covid restrictions such as social distancing and limits on household mixing were now inevitable. He hoped the Prime Minister understood the challenges London was facing — and would step in and support businesses.

And this is exactly the Catch-22 dilemma for an already weakened Boris Johnson, who has been warned by nearly half his backbench MPs that if he brings in further restrictions to deal with omicron, he is more likely to face a challenge to his premiership.

He suffered another personal blow on Saturday night when it was confirmed that a key ally, the Tory peer David Frost, was resigning from the cabinet with immediate effect for a number of reasons, including the Prime Minister’s decision to bring in Covid restrictions.

The government’s aim is to give 1 million doses a day — and it’s not quite there yet. So far 89 per cent of the adult population have had a first dose. This falls to 82 per cent for a second dose. But the booster jab — this is said to be vital to combat omicron — has so far been given to only 47 per cent.

On the last Sunday before Christmas, Oxford Street should be thronged with last-minute shoppers. The crowds are thinner and many restaurants have an abandoned look. Across the UK, many Christmas parties have been cancelled.

A senior government adviser, Prof. Neil Ferguson of Imperial College London, said there had been a significant surge in hospitalisation in the London region.