What could a national Covid lockdown in England mean?

Boris Johnson appears to have bowed to pressure from his scientific advisers for a new national lockdown in England, after they warned him that local measures were no longer enough and that the virus could kill 85,000 people this winter.
When could the UK go into lockdown?

The Times reported on Friday night that Boris Johnson is expected to announce the measures at a press conference on Monday, and that they could be introduced on Wednesday and last until 1 December. However, Downing Street confirmed it would hold a press conference at 4pm on Saturday.
What businesses may be forced to close?

Everything except essential shops and education settings, including nurseries, schools and universities, it has been suggested. The hospitality sector has warned that a full lockdown would “devastate” the embattled industry as pubs and restaurants would have to close their doors once more.
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Why has the decision been made?
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Confirmed cases are rising steeply, with an estimated 568,100 people in households becoming infected in the week ending 23 October. There are fears that deaths could potentially hit 500 a day within weeks and that the coronavirus could kill 85,000 people this winter, scientists on the Scientific Advisory Group for Emergencies (Sage) have warned.

The group has been concerned that the number of infections and hospital admissions is “exceeding the reasonable worst-case scenario planning levels at this time”. As of 30 October, there were 975 mechanical ventilation beds taken up by Covid patients in England, up from 285 at the beginning of the month. Of all beds, 10,708 were occupied by people with coronavirus, up from 2,069 on 1 October.

There have been 271,854 expected deaths from all causes since the beginning of the pandemic, plus 54,833 excess deaths, Public Health England data from 20 March to 16 October shows. On Tuesday, the UK coronavirus death toll passed 60,000. Covid-19 fatalities in hospitals as a proportion of all deaths was 12% in September, but there are fears it could spike. About 535,000 people per year die in the UK, less than 1% of the population. There were 50,100 excess deaths in the winter of 2017–18, higher than in any year since 1975–76.

A lockdown can stem the spread of the virus and thus reduce the reinfection rate. “The idea of a lockdown is to save lives primarily,” Prof John Edmunds, a member of Sage, told BBC Radio 4’s Today programme on Saturday. “I think the only real way that we have a relatively safe Christmas is to get the incidence right down.”