Last month, UK Prime Minister Boris Johnson made it clear that if the government's Plan A on encouraging COVID-19 boosters and free flu jabs fails to stop "unsustainable pressure" on the NHS, London will introduce Plan B.

Matthew Taylor, chief executive of the UK's National Health Service Confederation, has urged the government to swiftly roll out Plan B for anti-COVID winter measures to prevent a possible NHS crisis.

The call comes as Britain has seen the highest daily coronavirus death toll since March. Plan B envisages that the public would be urged to act more cautiously, mandatory vaccine passports could be used for mass events, and face coverings could be legally mandated in certain settings.