LONDON (BLOOMBERG) - British Prime Minister Boris Johnson has left the door open to another coronavirus lockdown this winter, warning that people must get their Covid-19 vaccinations and booster doses to avoid fresh restrictions.

A "new wave" of Covid-19 is spreading across Europe and forcing governments to reimpose tougher rules, Mr Johnson said at a televised press conference on Monday (Nov 15).

"History shows we cannot afford to be complacent."

Asked directly about the possibility of another lockdown this Christmas, Mr Johnson replied that there is nothing in the current data that signalled the need for restrictions, but warned that "clearly, we cannot rule anything out".

Any move to reintroduce pandemic restrictions would likely be politically perilous for Mr Johnson, who imposed an effective lockdown at the last minute over Christmas last year. Yet his comments are a marked change in tone from his insistence last month that there will be no curbs over the holiday season.

British chief medical officer Chris Whitty, standing alongside Mr Johnson, said British Covid-19 cases and hospitalisations had been "broadly flat" for some weeks.

But he said large parts of the National Health Service are under "very significant pressure" and likely to remain so over the winter.

Earlier on Monday, the British government said it is expanding its coronavirus vaccine booster programme to people in their 40s as it tries to head off another wave of infections.

But while Mr Johnson warned of the risk from Europe, some scientists argue that Britain - which has seen a high daily caseload since July - is actually ahead of the most recent wave sweeping the continent.