The first UK death with the Omicron Covid variant was today confirmed by Boris Johnson.
The Prime Minister told broadcasters at least one patient has died with the strain. Mr Johnson did not say where the death took place or any other details of the patient.
It comes hours after the government confirmed there were 10 patients with the new Omicron variant in England's hospitals.
Speculation has been continuing about whether Omicron is less lethal than the Delta variant. But shock data has shown Omicron cases doubling every two to three days - suggesting even if it is less lethal, it could still overwhelm the NHS.
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Last night the PM warned of a "tidal wave" and announced routine appointments would be scrapped in a bid to give a million booster jabs every day between today and New Year's Eve. The booking website crashed and lateral flow tests ran out until tomorrow.
At the same time, work-from-home guidance in England began today, and Mr Johnson faces a mass Tory revolt tomorrow over plans to force England's nightclub and event punters to show Covid passes from 6am on Wednesday.
Mr Johnson today refused three times to rule out introducing more restrictions before Christmas - as Scotland's Health Secretary said stricter rules are "inevitable".
Speaking during a visit to a vaccination clinic near Paddington, in west London, the Prime Minister said: "Omicron is producing hospitalisations and sadly at least one patient has been confirmed to have died with Omicron.
"So I think the idea that this is somehow a milder version of the virus, I think that's something we need to set on one side and just recognise the sheer pace at which it accelerates through the population.
"So the best thing we can do is all get our boosters."
Mr Johnson said Omicron now represents about 40 per cent of coronavirus cases in London and "tomorrow it'll be the majority of the cases" in the capital.
He told broadcasters: "The risk is plainly there, we can see Omicron spiking now in London and some other parts of the country.
MPs will vote tomorrow on forcing nightclubs, large events and indoor venues with capacities over 500 to demand Covid passes from their punters as a condition of entry.
People will have to either show they have had two doses of a vaccine, or that they have taken a recent lateral flow test and it has come back negative. People will be able to show a text or email from the NHS testing service.
MPs will also vote tomorrow on face mask laws in theatres and cinemas that came in on Friday in England. More than 60 Tory MPs could rebel - but the measures will pass because Labour is backing them.
Mr Johnson said MPs thinking of rebelling against Plan B measures needed to recognise there was "no room for complacency" in dealing with Omicron.
He said: "I think that what everybody needs to recognise is a couple of things - that Omicron is a very serious risk to public health, and that it's spreading very fast, and I think there's no room for complacency."
The PM admitted "it became clear on Friday that two jabs were not enough" to hold off an Omicron wave, and urged adults to get their boosters - despite the website crashing.
Despite this, people will be able to show they've had just two doses to get into a crowded venue. Whether to up this to three doses is being kept under review.