Boris Johnson has suggested he could impose a third national lockdown on England.
The prime minister left the prospect of a January lockdown open if cases “flare up again” over Christmas.
Johnson was discussing plans for temporarily easing household mixing restrictions over the festive period.
He told MPs in the House of Commons on Monday: “I can’t say that Christmas will be normal this year, but in a period of adversity, time spent with loved ones is even more precious for people of all faiths and none.
“We all want some kind of Christmas, we need it, we certainly feel we deserve it.
“But what we don’t want is to throw caution to the winds and allow the virus to flare up again, forcing us all back into lockdown in January.”
It came after Johnson confirmed England’s second national lockdown will be replaced by a revised three-tier system after 2 December.
Over the festive period, it is understood Johnson will permit three households to mix over a period of five days in the UK. A final announcement is expected on Tuesday.
Watch: Boris Johnson announces return to three-tier COVID restrictions
The prime minister said a plan is being formulated with the devolved governments of Scotland, Wales and Northern Irelands to “minimise the risk”.
However, he again warned: “This virus is obviously not going to grant us a Christmas truce, it doesn’t know it’s Christmas.”
The PM also suggested people who visit or host elderly relatives will be doing so at their own risk: “Families will need to make a careful judgement about the risk of visiting elderly relatives.”
Johnson, meanwhile, warned the revised tier system will be “tougher” and include more regions in the stricter Tiers 3 and 2. A list of areas is set to be published on Thursday.
Watch: 8 exceptions to England's second national lockdown