No 10 is increasingly worried that hospitalisations and deaths among double-vaccinated people could rise due to waning immunity as an estimated 4.5 million people have failed to get their booster shots despite being eligible.

Downing Street sources told the Guardian that the gap between those eligible and those jabbed was too wide, ranking it as their major concern ahead of the winter months.

They acknowledged more needed to be done to encourage take-up as waning immunity meant more double jabbed people could get sick and were at greater risk of dying without the extra protection of the boosters.

The UK reported 293 deaths with Covid on Tuesday – the highest level since February – although the figure included all NHS England deaths from Monday owing to reporting delays. There were 33,865 daily reported cases, a drop from more than 40,000 in recent days, and 9,538 people were in hospital with Covid on Monday compared with 6,467 a month ago.