Boris Johnson has warned that “storm clouds are gathering" over parts of Europe with a “new wave” of COVID sweeping through the continent.
The prime minister urged people to come forward for COVID booster shots to avoid the need for a Christmas lockdown.
The booster programme has been extended to the over-40s and is already available for anyone in an at-risk group.
On Monday, Johnson told a Downing Street press conference parts of Europe were being hit hard by COVID.
He said: “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.”
Some Western European countries have brought back lockdown measures to tackle the new waves.
Austria is among the hardest-hit by Europe's new wave of infections, with a case rate of 1200 per one million people.
On Monday, the country entered a lockdown for those not vaccinated against coronavirus, with reinforced police checks to ensure compliance.
The aim is to counter a surge in infections to record levels fuelled by a full vaccination rate of only about 65% of the population, one of the lowest in western Europe.
The Netherlands also returned to a partial lockdown last Saturday after the government ordered restaurants and shops to close early and barred spectators from major sporting events in an effort to contain the rapid surge in cases.
Over 100,000 new infections were registered in the week through Monday, the highest level for a single week since the start of the pandemic.
Germany's coronavirus infection rate has also risen to its highest level since the start of the pandemic.
The seven-day incidence rate – the number of people per 100,000 to be infected over the last week – rose to 303 from 289 the previous day, figures from the Robert Koch Institute showed.
The three parties in talks to form a coalition government plan to tighten proposed restrictions to tackle the spread of the new wave of infections.
Professor Chris Whitty warned cases were increasing across Europe.
He told the Downing Street Press conference: “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.
“We all knew – everywhere in Europe we knew – that as we went into winter, into the typical respiratory virus/flu season, that the risks would be greater, and I think this is a demonstration of the fact that we’re beginning to see a winter respiratory effect.”
There have been concerns over the speed of the COVID booster programme in the UK, with analysis by Yahoo News UK showing almost five million people who are eligible for a booster have not yet had one.
Watch: PM pleads for Brits to take booster jabs to avoid 'tragedy'