Any fresh Christmas lockdown and Covid “storm clouds” forming in Europe can only be avoided by those eligible getting their booster vaccinations, the country has been warned.

Significant numbers of unvaccinated people across Europe are dying from coronavirus, England’s chief medical officer Professor Chris Whitty said at a Downing Street briefing on Monday.

And he said if the number of deaths was replicated in the UK, winter restrictions may need a rethink.

Boris Johnson said while the data did not show, at the moment, that any additional measures were needed, he could not rule out a lockdown over Christmas if case rates rose.

The UK Government announced on Monday that those aged over 40 would be invited to receive booster jabs in coming weeks.

Mr Johnson said: “It would be an utter tragedy if, after everything we have been through, people who had done the right thing by getting double vaccinated ended up becoming seriously ill or even losing their lives because they allowed their immunity to wane.”

Prof Whitty warned that “we’re beginning to see a winter respiratory effect” of other viruses impacting on the coronavirus pandemic and putting “substantial pressure” on the NHS.

He said: “There has already been a very significant increase in eastern Europe which is still ongoing, with significant numbers of people dying, in particular among the unvaccinated.

“That has now moved westward and, as you can see, is now increasing significantly, also in many western European countries.”

The PM added: “We don’t yet know the extent to which this new wave will sweep up on our shores but history shows that we cannot afford to be complacent.”

He said: “Those countries with lower vaccination rates have tended to see bigger surges in infection and in turn been forced to respond with harsher measures, while those countries with higher vaccination rates have so far fared better.

“It shows us that if we want to control the epidemic here in the UK and if we want to avoid restrictions on our daily lives we must all get vaccinated as soon as we are eligible.”

Despite the concern over the winter months, Mr Johnson said there was nothing currently in the data to suggest the country needed to move to Plan B of Covid measures.

But Prof Whitty said a rethink on whether restrictions should be introduced would be needed if case numbers increased on the scale seen in Europe.

He said the numbers were “broadly flat”, adding: “There is substantial pressure on the NHS and that is widely recognised by everybody, ministers obviously included.

“But in terms of the Covid numbers, they’re not currently going up in the kind of numbers you’re seeing in continental Europe, but obviously if they did that would be a situation where we would have to look again at what the situation is at that stage.”

He added: “I think we have got a difficult winter ahead of us. I think that is a widely accepted situation.

“The NHS is a remarkably resilient organisation. But nevertheless everybody would accept that large parts of it – particularly the ambulance system but there are others, A&E and others – are under significant pressure, and I’m afraid are likely to remain so over the winter period, which is why all health staff would reiterate the point the PM has made about encouraging people to get vaccinated.”

Asked whether he could guarantee there would not be another lockdown over Christmas, Mr Johnson told the press briefing: “Clearly we cannot rule anything out and the most important thing people can do to prevent further NPIs from being taken is to – non-pharmaceutical interventions that is, further restrictions – get the boosters.”

The Government said a further 47 people had died within 28 days of testing positive for Covid-19 as of Monday, bringing the UK total to 142,945.

Separate figures published by the Office for National Statistics show there have been 167,000 deaths registered in the UK where Covid-19 was mentioned on the death certificate.

As of 9am on Monday, there had been a further 39,705 lab-confirmed Covid-19 cases in the UK, the Government said.

Mr Johnson said “GPs are hitting it out of the park again” delivering booster vaccines with numbers rising.

He added: “It’s starting to build a lot of momentum, but we need to see those 50-plus groups and the 60-plus groups – who can also wind up in hospital very, very easily – getting their booster as soon as you’re called forward to get it.

“That’s the best protection we can have.

“But to repeat, I see nothing in the data at the moment that makes me think we have to go to further measures.”

Ministers accepted on Monday a recommendation from the Joint Committee on Vaccination and Immunisation (JCVI) that the booster programme should be extended to include people aged 40 to 49.

Second doses for 16 and 17-year-olds have also been approved after the JCVI said this group should be offered a second jab of the Pfizer/BioNTech jab 12 weeks after they received the first.

The JCVI said that the broadening of the booster campaign and the offer of a second jab to 16 and 17-year-olds will “help extend our protection into 2022”.

A total of 50,582,504 first doses of Covid-19 vaccine had been delivered in the UK by November 14, Government figures show. This is a rise of 22,938 on the previous day.

Some 46,027,909 second doses have been delivered, an increase of 17,048.

A combined total of 12,860,751 booster and third doses have also been given, a day-on-day rise of 217,349.

Separate totals for booster and third doses are not available.