Long queues were seen outside walk-in vaccination centres across the UK on Monday as people queued for their booster vaccine doses, even as the government's work from home guidance came in force as part of measures to tackle the "tidal wave" of the Omicron variant of COVID-19.

British Prime Minister Boris Johnson warned of a tidal wave of the highly transmissible variant on its way as he issued an urgent televised address on Sunday night.

He announced an enhanced Omicron Emergency Boost campaign, which sets an end of the year deadline for all adults aged over 18 to be offered a third top-up dose of a COVID-19 vaccine. This brings forward his previous timeline of January 2022 for this target in an effort to build a "wall of vaccine protection" against the new variant.

"I am afraid we are now facing an emergency in our battle with the new variant, Omicron, and we must urgently reinforce our wall of vaccine protection to keep our friends and loved ones safe, said Johnson.

"No-one should be in any doubt: there is a tidal wave of Omicron coming, and I'm afraid it is now clear that two doses of vaccine are simply not enough to give the level of protection we all need. But the good news is that our scientists are confident that with a third dose a booster dose we can all bring our level of protection back up, he said.

UK Health Secretary Sajid Javid reiterated the message on Monday, adding that the Omicron variant is "spreading at a phenomenal rate" and infections are continuing to double every two to three days.

We are clearly once again in a race between the vaccine and the virus," he said.

Ten people in England are in hospital with the new COVID variant, first detected in South Africa, but no deaths have yet been reported related to Omicron in the UK.

Meanwhile, people in England are now expected to work from home if they can, as part of the government's Plan B guidance. The change brings England in line with Scotland, Wales and Northern Ireland. Plan B also means stricter face covering rules for indoor spaces and compulsory COVID vaccination pass for venues will come in from Wednesday.

Members of Parliament are expected to vote on the new measures on Tuesday. One of the three votes in the House of Commons will be on COVID vaccine passes, and could be opposed by Boris Johnson's own 60 Tory MPs. However, all parliamentary votes are expected to pass as the Opposition Labour is backing the government.

The UK's COVID alert level has been raised to level four which means a high or rising level of transmission for the first time since May due to the spread of Omicron. Early data suggests that getting a third booster dose gives around 75 per cent protection against symptomatic infection against Omicron.

More than half a million booster jabs and third doses were administered by the National Health Service (NHS) in the UK on Saturday, the second day that has happened since the booster rollout began in the country.

A further 1,239 new cases of Omicron were announced in the UK on Sunday, bringing the total number of UK Omicron cases to more than 3,000 and the total number of COVID infections to 48,854.