Face masks being worn in other settings not currently required, such as restaurants and pubs, is another option, as is expanding the venues that must ask for Covid passports.

Then there is a string of more interventionist moves, which can be identified by looking back at what restrictions were in place earlier in the year.

These would, in theory, be steps like limiting the amount of social contact – such as putting hard caps on group gathering numbers – and bringing in social distancing rules.

Downing Street sources made clear yesterday these are not currently being actively considered, with ministers for months arguing the economic impact of such steps would be significant.

Boosters 75pc effective against mild omicron

Health officials revealed on Friday that booster jabs give up to 75 per cent protection from mild omicron infection, compared to 95 per cent protection against delta.

The UKHSA conducted the world’s first analysis to calculate vaccine effectiveness against omicron and revealed that after two doses, vaccine effectiveness against mild disease is just 40 per cent for Pfizer. Two doses of AstraZeneca were found to give “no protective effect” four months after the second dose.

The agency also revealed today that omicron is up to eight times more likely to reinfect someone who has already had Covid than delta, with seven per cent of omicron cases being re-infections.

The highly transmissible variant is also more of a danger in the household, and a person living with an infected person is more than three times as likely to catch it off them than they would be if it was delta.

Overall, a person is twice as likely to pass omicron on to someone else than they are for delta, the UKHSA found.