Returning to a tiered system of coronavirus restrictions next month will cause infections to rise to the levels which prompted England to enter its second lockdown, the government's scientific advisers have warned.
In newly-released documents, the Scientific Advisory Group for Emergencies (SAGE) said the country's coronavirus reproduction rate - or R number - is likely to fall below 1 during the four-week lockdown.
But the experts said that infections will "return to the same rate of increase" as before national restrictions were imposed on 5 November if the country returns to its previous three-tier system.
Prime Minister Boris Johnson has insisted the latest lockdown will end on 2 December but it remains unclear what restrictions will be in place over the Christmas period.
In its document, SAGE said England's lockdown is "likely to reduce R to less than 1" and the number of hospital admissions and deaths "would be expected to fall until at least the second week of December".
But it warned that the "longer-term outlook" depends on "policies over the festive period".
"If England returns to the same application of the tiering system in place before 5th November, then transmission will return to the same rate of increase as today," SAGE said in the document dated 4 November.
If the R value is above 1 then the COVID-19 epidemic continues to grow, but if it is below 1 it shows the outbreak is in retreat.
The tier system in England saw regions placed in three separate tiers classed as "medium", "high" or "very high" depending on their rate of coronavirus infections.
Under the "medium" tier 1 restrictions, areas were told to follow the rule of six if meeting indoors or outdoors and pubs and restaurants were ordered to close at 10pm.
The "high" tier 2 restrictions also forced pubs and restaurants to shut at 10pm but banned households mixing indoors, with the rule of six applying when people met outdoors.
Under the "very high" tier 3 restrictions, no households could mix indoors or outdoors in hospitality venues or private gardens and the rule of six applied in open public spaces such as parks and beaches.
Pubs and bars not serving meals were forced to close and people were urged not to travel in and out of the area.
In its document, SAGE said that initial analysis suggested tier 3 measures in England had a "noticeable impact on transmission, but it is not yet clear whether they have been sufficient to reduce R below 1".
Following England's second lockdown, it was revealed on Friday that the UK's R number has fallen slightly to a maximum of 1.2.
The figure is now between 1.0 and 1.2 - down from between 1.1 and 1.3 last week.
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Experts believe the R value is below one in some places, particularly in parts of Wales and potentially parts of Scotland and the north west of England.
It is hoped that R will drop in more places next week or the week after, as people remain under lockdown restrictions.
