A major incident has been declared in London and more than 10,000 new Omicron cases have been confirmed in the UK, as the variant surges across the country.
A further 90,418 daily Covid cases have been reported across the UK on Saturday, after days of record highs.
Scientific advisers have warned England’s hospital admissions could reach 3,000 a day without new measures.
London Mayor Sadiq Khan said the major incident in the capital showed “how serious things are”.
Ministers received a briefing on the latest Covid data on Saturday afternoon – with a meeting of the Cobra emergency committee due to be held this weekend.
Restrictions “similar in scale to the national lockdown” would be required to keep hospital admissions from Covid below previous peaks, modelling advisers to the government said, in newly-released minutes.
Without intervention beyond current Plan B rules in England, hospitalisations could reach 3,000 a day, members of the Scientific Advisory Group for Emergency (Sage) added.
Latest daily data showed 900 patients with Covid were admitted to hospital in the UK.
The Sage advisers said further measures to curb the spread of Omicron could include “reducing group sizes, increasing physical distancing, reducing duration of contacts and closing high-risk premises”.
The advisers said indoor mixing was the “biggest risk factor” for the spread of Omicron, and that large gatherings risked creating “multiple spreading events”.
They warned delaying the introduction of stricter measures until 2022 would “greatly reduce the effectiveness of such interventions and make it is less likely that these would prevent considerable pressure on health and care settings”.
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