The British government on Tuesday released a COVID-19 Autumn and Winter Plan, outlining the possible measures and restrictions the country may see towards the end of this year.

The plan, unveiled by British Prime Minister Boris Johnson, said there is "significant uncertainty" about what will happen later this year and there is a "plausible" risk of cases rising to an extent that would place the National Health Service (NHS) under "unsustainable pressure".

Vaccine passports and the legally mandated wearing of face masks are part of a "Plan B" drawn up to tackle COVID this winter if the NHS comes under unsustainable pressure, in addition to the "Plan A" - promoting vaccines and continuing testing and isolation rules.

Johnson said "Plan B", with measures including face masks, would aim to prevent the NHS being overwhelmed.

Asked in what circumstances would he consider moving from Plan A to the stricter Plan B, the prime minister said he would consider the risks and state of the disease through real-time data.

Johnson said the vaccine programme is being intensified and the government is "motoring ahead" with the booster program. This will build even higher walls of vaccine protection, he said.

Earlier Tuesday, the British government announced that booster COVID-19 jabs will be offered to people aged 50 and over, those in care homes, and frontline health and social care workers. Chief medical officers of Britain's all four nations confirmed on Monday that children aged 12 to 15 will be offered the COVID-19 vaccine.

"The winter plan for COVID-19 serves as a warning about the way that we control the virus 18 months after the pandemic first hit. Rolling out the best line of defence, in the form of vaccine boosters and jabs for younger teenagers continues to put the emphasis on 'COVID, but not too badly'," said Simon Clarke, associate professor in cellular microbiology at the University of Reading.

More than 89 percent of people aged 16 and over in Britain have had their first dose of vaccine and more than 81 percent have received both doses, the latest figures showed.

To bring life back to normal, countries such as Britain, China, Germany, Russia and the United States have been racing against time to roll out coronavirus vaccines.