The idea of a normal Christmas this year "is wishful thinking in the extreme" as the Covid crisis worsens, a Government scientific adviser has warned.
Professor John Edmunds, a member of the Scientific Advisory Group for Emergencies (Sage), said "radical action" is needed to stem the second wave of coronavirus cases - particularly in regions with high incidence of the virus.
Prime Minister Boris Johnson remains "hopeful" that "some aspects" of life may be back to normal by Christmas, his spokesman said.
He added: "We've been clear about the ambition to ensure that people may celebrate Christmas as a family this year."
It comes after Chief Secretary to the Treasury Stephen Barclay said he hoped families would be able to spend Christmas together - even if things are not exactly the same.
Mr Barclay told BBC Radio 4’s Today programme: “I would describe it as a shared endeavour for all of us.
“All of us want to be able to enjoy Christmas with our families. And that’s why there is a common purpose here to get the virus down.”
ITV News pushed Mr Barclay on why the government had failed to introduce a circuit-break style lockdown, despite advice from government scientists to do so.
The MP said the current local approach to restrictions were a "balanced set of measures" and said a national style lockdown "would not be the right approach".
But Prof Edmunds - who warned MPs on Wednesday that tens of thousands of deaths could occur during this wave of the pandemic - said further measures are needed to bring cases down.
He told the PA news agency that a circuit-breaker is needed across the whole country, or at least in areas where incidence is high.
"The only way that we can have a relatively safe and normal Christmas is if we take radical action now to reduce incidence – at the very least in high incidence areas – and keep the incidence low across the country by implementing a package of measures to reduce social contacts," he said.
Prof Edmunds spoke to ITV News Political Editor Robert Peston in September about the prospects for Christmas during the Covid crisis:
"The notion that we can carry on as we are and have a Christmas that we can celebrate normally with friends and family is wishful thinking in the extreme."
On Friday, sweeping new restrictions were imposed on millions more people across the country.
Greater Manchester moved into the highest alert level in England, Tier 3, while Wales' two-week “firebreak” lockdown gets underway on Friday evening.
It was announced Warrington too would move into Tier 3 restrictions, while it is thought Nottinghamshire too will join the highest level alert.
Covid tiers: - What are the differences between each alert level?
Medium (Tier 1) - Rule of six applies indoors and outdoors. Pubs and restaurants close at 10pm.
High (Tier 2) - Households must not mix indoors in any setting including pubs and restaurants. Rule of six applies outdoors
Very high (Tier 3) - Households must not mix indoors, or in private gardens. Rule of six applies in outdoor spaces including parks. Pubs and bars which don't serve meals will be closed
But Labour criticised the Chancellor for bringing in the measures "too late" and only after the changes hit London.
It came as Prime Minister Boris Johnson acknowledged that the Covid Test and Trace system, which he previously promised would be “world-beating”, needs to be improved.
He said on Thursday that turnaround times for tests need to be faster, after it emerged that just one in seven people having a test at a centre get their result back in 24 hours.