UK scientists are set to announce an expansion of the Covid-19 booster vaccine programme as nine cases of the Omicron variant have been confirmed across the country.

Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), said experts have been looking at extending boosters to the under-40s and whether the time interval between the second and third doses of the vaccine should be cut.

A decision is expected to be announced on Monday afternoon, at the same time as an urgent meeting is held of health ministers from the G7 group of nations to discuss the new Omicron variant.

According to the World Health Organisation (WHO), preliminary evidence suggests Omicron carries a higher risk of reinfection though it is not yet clear how transmissible it is or whether it can evade vaccine protection.

The UK now has nine confirmed cases of the variant after the Scottish government announced on Monday morning it had discovered four cases in Lanarkshire and two in the Greater Glasgow and Clyde area.

One other case has been identified in Brentwood, Essex, with another in Nottingham, while a third case was detected in England on Sunday in a person with travel links to southern Africa who visited Westminster before leaving the country.

Scotland’s Deputy First Minister John Swinney said that some of the Omicron variant cases identified in Scotland have no travel history, which suggests there is a degree of community transmission.

Meanwhile, in Essex, where one case has been found, students at a school are being tested for the variant as part of a targeted drive to identify close contacts.

From Tuesday, the wearing of face masks is set to be compulsory in shops and on public transport, while PCR tests will be brought back in for travellers returning to the UK.

Asked on BBC Breakfast about the six new cases discovered in Scotland, Prof Harnden said: “I think it’s almost inevitable that we’re going to see many, many more cases than we’ve seen before.

“The key question is whether this virus has a transmission advantage over the Delta, which is the prevalent virus at the moment.

“Vaccines can do heavy lifting, but they can’t do all the lifting and actually social distancing measures – that’s wearing face masks, distancing, ventilation … and measures like that – are important as well.

“So I think we will see some more of these measures and I know the Government have announced face masks in public transport already and that may be extended, but we’ll just have to wait and see whether this Omicron virus takes a big hold in this country and how big a problem it actually is.

“It’s obviously a worrying development, but I don’t think there’s any need for anyone to panic. What they do need to do, though, is get vaccinated.”

This virus has a nasty habit of surprising us, we know that.

Elsewhere, health minister Edward Argar defended the Government’s action so far to limit the spread of the variant, adding he is not expecting further restrictions in the run-up to Christmas.

Asked if the Government might tighten the rules even further in the next three weeks, Mr Argar told Sky News: “It’s not something I’m anticipating.”

He argued that the Government had taken swift action over the new coronavirus variant, telling BBC Radio 4’s Today programme: “I think we are very much on the front foot with this.

“This virus has a nasty habit of surprising us, we know that. But we’ve also got to keep a sense of proportion and cool, calm heads as we do that scientific work to understand what may or may not be needed in the future.”

On whether the Government should be moving to its Plan B, Mr Argar said: “In the current circumstances, we don’t see that that is needed at this point because there is no evidence yet that the vaccine is ineffective against this new variant.”

He added: “I don’t think we are in a position yet to understand impact on vaccines and on hospitalisations and therefore, rather than automatically going to what some will call for which is very, very heavy restrictions, or what others will call for, which is nothing at all and wait and see, we’ve struck, I think, a reasonable and proportionate balance in the middle, moving swiftly to put in place measures to slow it down while we understand it. And that should hopefully only take a few weeks.”

However, deputy Labour leader Angela Rayner said people should be wearing face coverings at indoor hospitality venues, a suggestion backed by the British Medical Association (BMA).

She told Sky News: “We think that in hospitality settings that people should be wearing a mask. I got the train here yesterday evening and it was absolutely rammed, you couldn’t even stand up, it was so full, and nobody, very few people, were wearing a mask on that train.

“It’s so important that people wear masks when they’re indoors, in arenas where they’re meeting people and… mixing in large numbers. People should be wearing their masks.”

On wearing masks in pubs, she said: “I think people should… especially if you’re moving around the pub, people should be wearing their masks in hospitality settings. If you’re (in) an indoor setting, there’s no distinction between a pub, sitting in a pub, or sitting on a train, or sitting in a hospital.

“It’s still a venue that’s indoors and we should be taking the necessary measures to protect people around us.”

Dr Chaand Nagpaul, chairman of council at the BMA, also called for further mask-wearing.

He told Good Morning Britain: “What we believe is that there should be mask-wearing in all settings which are enclosed and indoors.

“Now clearly, that doesn’t apply to people who are eating out, but it should apply to staff, for example, in restaurants and bars so that when you are close to a customer, when you’re in direct line of a customer, maybe a few feet away, and you’re speaking perhaps loudly, you reduce the chance of infecting others.

“This isn’t just about the public, it’s also about staff and employers as well, because if they have staff who become infected, staff who are ill and self-isolating, that will also affect the economy.

“So there is a reason for doing this for both customers and employers.”

Meanwhile, Professor Sir Mark Walport, who is a member of the Scientific Advisory Group for Emergencies (Sage) advising Government, told Sky News there was “good cause to be concerned” about Omicron.

He said it “makes sense to try and hold it back” though it will be “impossible to stop it spreading around the world if it is much more infectious than the Delta variant”.

Sir Mark said the most important thing people in the UK could do was to have vaccines and take measures such as wearing masks.