While Johnson has always reserved the right to impose tougher measures,he spent the past two months saying a second lockdown would be a"disaster"and inflict"misery"on the public.

The government's powerful Scientific Advisory Group on Emergencies (SAGE) urged him to authorise a two-week'circuit-breaker'lockdown in September but the Prime Minister rejected the advice.

"We've had to listen to all kinds of scientific advice,"Johnson said on Saturday."But we also have to balance that scientific advice with the consequences on people's lives,their mental health and their livelihoods."

Labour and other critics said the delay meant England would instead endure a longer and more economically damaging lockdown that will be less successful in lowering the death toll.

Government experts have found that even the thousands of extra hospital beds created to handle the pandemic would be overwhelmed in most parts of England by late November and early December.

Ten hospitals already have more patients now than the first wave and 14 currently have more than half.

Johnson said allowing the National Health Service to be overrun would be a"medical and moral disaster".

"Doctors and nurses would be forced to chose which patients to treat,who would get oxygen and wouldn't,who would live and who would die,"he said.

"Doctors and nurses would have to choose between saving COVID patients and non-COVID patients."

The number of daily deaths during the first wave peaked at about 1000 a day. The latest forecasts show the winter wave would kill 1000 people a day from December 8,and eventually claim 85,000 lives by March.

Johnson declined to guarantee the restrictions would be lifted from December 2.

"Christmas is going to be very different this year,perhaps very different. But it is my sincere hope that by taking action now we can allow families to be together,"the Prime Minister said.

The UK has recorded an average of about 23,000 new cases per day for the past week but the figures do not capture the true number of infections.

The Office for National Statistics on Friday said there were 51,900 new infections in England alone each day. Another study by Imperial College London put the figure at 96,000.

Australia has recorded 27,590 cases in total since the pandemic began.

"We've got to be humble in the face of nature and in this country,alas,the virus is spreading even faster than the reasonable worse-case scenario of our scientific advisors,"Johnson said.

The worst-case scenario is not a forecast but is used by government officials and National Health Service managers to plan for the second wave.

Professor John Edmunds,an epidemiologist who sits on SAGE,warned the country should brace for a grim winter.

"It is really unthinkable now,unfortunately,that we don't count our deaths in tens of thousands from this wave,"he said on Saturday."The issue is,is that going to be low tens of thousands if we take radical action now or is that going to be the high tens of thousands if we don't?"

Experts say lockdowns are most effective when introduced early in the course of an outbreak.

National lockdowns were this week ordered in Germany,France,Austria and Belgium,where infections have been surging. Borders within the European Union are still open but travel is discouraged. And like Britain,schools will remain open in those four countries.

Chancellor Angela Merkel announced a lockdown on Wednesday when the number of fortnightly infections there hit 195 per 100,000 people. The equivalent figure in the UK is 451.

"The idea there is a perfect time to act is a misapprehension,"chief medical officer Chris Whitty said on Saturday.

The lockdown will be put to a vote in the House of Commons on Wednesday before coming into force on Thursday.

However,many Conservative MPs oppose lockdowns and may vote against the government. Johnson would be able to rely on support from Labour to get the plan through Parliament. Labour had urged Johnson to embrace a two-week lockdown earlier this month.

British media said backbenchers had gone"nuclear"about Johnson's decision and the anger inside the party was"volcanic".

Jeremy Hunt,the former health secretary and Johnson's rival in last year's Tory leadership contest,took a gentle swipe at the government's response to the crisis but backed the Prime Minister's decision.

"Many will debate whether we could have avoided getting to this point but in a pandemic I would rather a PM brave enough to change his mind than one who risks lives by sticking his head in the sand,"he said.