The warning comes after scientists from the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG), which advises the Government, held an emergency meeting to discuss the new Omicron variant, also known as B.1.1.529. The experts concluded that the variant could have "very serious conseqeunces" for the UK. Note of the meeting from last Thursday, published online on Monday, said that "if introduced into the UK, B.1.1.529 would likely be capable of initiating a new wave of infections".

       The experts, whose meeting has been observed by a key Department of Health official and England's deputy chief medical officer Jonathan Van-Tam, also said: "We cannot exclude that this wave would be of a magnitude similar, or even larger, than previous waves.

       "Although data on disease severity associated with B.1.1.529 are not yet available, a large wave of infections will be accompanied by a wave of severe cases and the subgroup cannot rule out that this may be sufficient to overwhelm NHS capacity."

       Government sources claimed they have already listened and responded to NERVTAG's advice, having taken action with compulsory mask wearing, boosters, self-isolation rules, and travel restrictions.

       Mr Johnson has reintroduced compulsory mask-wearing in England in shops and on public transport, said that people have to self-isolate if they have been a contact of someone infected with the Omicron variant, and has brought back day two PCR testing for anyone who enters the UK from abroad.

       He has also extended the rollout of booster jabs.

       This is a breaking story. More to follow.