Boris Johnson has said it is "absolutely crazy" that people are being put into intensive care because they are refusing the Covid vaccine.
The prime minister told a news conference on Tuesday afternoon that there were ample slots for people to get vaccinated but some people were still not being jabbed.
His chief medical officer Chris Whitty added that he was "saddened" by the numbers of unvaccinated people in intensive care, adding that "the great majority of them are not anti-vaxxers".
It comes after the prime minister said he was minded to stick to the government's so-called Plan B approach and not bring in further restrictions to fight the Omicron wave.
Mr Johnson told reporters: "How absolutely crazy it is, absolutely crazy, that there are two million slots this week for people to get vaccinated and yet the majority of people in ICU for Covid are not vaccinated - 61 per cent.
"It is sad but it is also a huge opportunity for us to correct it."
Unvaccinated people are disproportionately likely to become severely ill from Covid and require hospital treatment or even die.
Professor Sir Chris Whitty has said there is "misinformation" on the internet "a lot of it deliberately placed" about the potential side effects of the jabs.
"In so far as I am frustrated it is simply people deliberately trying to scare away fellow citizens from something that is potentially going to be life-saving for them," he added.
Meanwhile Patrick Vallance, the government's chief scientific officer, said it would be "untenable" for everyone to be given booster shots "every three or six months".
He added: "That is not the long-term view of where this goes to. There may be some people who will require an additional dose, but longer term I would think that as this becomes a disease which is endemic... it will be something like an annual vaccine like flu or of that order."
Sir Patrick also said: "The good news is that as you get vaccinated more the immune system broadens its response so that it covers more variants."
Over 90 per cent of people over 12 years old in the UK have had their first Covid vaccine dose as of the New Year, with more than 51.7 million Covid vaccines delivered up and down the country.
The government says there has been an almost 50 per cent surge in people coming forward for their first Covid vaccine as the booster programme continues.
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