Coronavirus lockdown: England considering stricter nationwide restrictions
The Prime Minister is expected to announce the measures for England - which could see everywhere except essential shops and education settings closed for a month
Mr Johnson has so far resisted pressure to introduce nationwide restrictions, opting instead for a localised tier system.
Government scientific advisers believe it is now too late for a two-week national circuit-breaker to have enough of an effect.
Professor Calum Semple, a member of the Scientific Advisory Group for Emergencies (Sage), speaking in a personal capacity, told BBC Radio 4's Today programme: "For the naysayers that don't believe in a second wave, there is a second wave.
"And, unlike the first wave, where we had a national lockdown which protected huge swathes of society, this outbreak is now running riot across all age groups."
Fellow Sage scientist Professor John Edmunds said the only way to have a "relatively safe" Christmas is to take "stringent" action now to bring the incidence of the virus "right down".
He said the current strategy "guarantees high incidence across the country over the winter", and that, while restrictions do not have to be national, there is a danger that, even in the South West where cases are lower, hospitals will be under pressure within weeks.
"I think the only real way that we have a relatively safe Christmas is to get the incidence right down because otherwise I think Christmas is very difficult for people - nobody wants to have a disrupted Christmas holiday period where you can't see your family and so on," he said.
"So I think the only way that that can be safely achieved is to bring the incidence right down, and in order to do that we have to take action now and that action needs to be stringent, unfortunately."
His comments came after a senior Government scientific adviser said it is "definitely too late to think that the two-week circuit-breaker on it own will sort this out".
"It would bring it down a bit but it wouldn't be enough to bring (the R value) right down.”
The Government's plan was briefed to selective newspapers on Friday evening, sparking criticism from John Apter, chairman of the Police Federation of England and Wales, which represents 120,000 officers.
He said such an approach increased pressure on the emergency services, tweeting: "To those briefing selective media on a potential national lockdown please understand the impact this has.
"It creates a media frenzy, causes confusion and ahead of any official announcement encourages some to make the most of their pre-lockdown time. This is not a good mix!"
The proposed restrictions have led to fresh calls for more financial help for affected businesses, on the day the furlough scheme closes and is replaced by the Chancellor's Job Support Scheme (JSS).
Northern Ireland pubs and restaurants were closed for four weeks starting on October 16 with the exception of takeaways and deliveries. Schools were closed for two weeks.
Wales is currently under a "firebreak" lockdown, with leisure, hospitality and tourism businesses closed, and in Scotland the majority of people will be under Level 3 of a new five-tier system from Monday.
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