Family doctors across England are to begin vaccinating their patients against Covid-19 as health experts issued fresh warnings about a rise in cases caused by Christmas socialising.

GP practices in more than 100 locations are to start administering the Pfizer/BioNTech vaccine on Monday afternoon, with the over-80s among those called up to receive the jab.

It comes as London and Essex could go into Tier 3 amid concerns about rising infection rates.

Care home residents in Scotland began to receive the Pfizer vaccine on Monday, while those in England’s care homes can expect to see roving teams administer the jab from later this week.

Dr Nikita Kanani, director of primary care at NHS England, urged all those expecting to receive the vaccine to be patient and wait to be called up by their GP.

“There’s a huge range of things that general practices are already doing so if we can ask for people to just wait a moment and wait to be contacted that would be very appreciated,” she told BBC Radio 4’s Today programme.

Meanwhile, Business Secretary Alok Sharma told BBC Breakfast that arrangements are in place “to make sure the distribution of vaccines is not in any way disrupted” in the event of a no-deal Brexit.

He added that there will be “some millions” of the Pfizer/BioNTech vaccine in the UK before Christmas.

“We are going as fast as we can in terms of the vaccination programme,” he said.

The vaccination centres will operate from doctors’ surgeries or community hubs in villages, towns and cities, and come after more than 70 UK hospital hubs began administering jabs.

GP leaders have warned that the requirement to observe patients for 15 minutes after the jab poses a challenge for some practices with limited space, especially while also observing social distancing rules.

Some GP surgeries have turned to their communities to ask for help, requesting outdoor marquees or tents that can be heated so the observations can take place outside.

It comes as experts issued fresh warnings about families and friends meeting for Christmas – which is widely expected to result in a spike in cases.

Under the rules, people will be able to form a “Christmas bubble” between December 23 and 27 made up of people from no more than three households.

Professor Devi Sridhar, chairwoman of global public health at Edinburgh University, warned that the virus “spreads like cigarette smoke” indoors and people could easily fall ill.

She told ITV’s Good Morning Britain: “This is the worry about Christmas because once you enter somebody’s home, you’re probably going to get the virus if someone else there has it.

“The three things I’d say to people is, first, we have a vaccine right around the corner – Pfizer is already being rolled out, AstraZeneca is on its way.

“So within weeks people are going to be vaccinated and safe, who otherwise would be at risk.

“Secondly, NHS staff are exhausted, they are begging people to be cautious, to not get infected, because they’re the ones in the end who have to be showing up in hospital on Christmas Day, on Boxing Day and New Year’s and actually having to take care of everyone that comes through.

“And third, look at what happened in the States with American Thanksgiving.

“You only have to read the stories, look at the figures to see what happens if people aren’t cautious right now over the Christmas period.”

Gabriel Scally, professor of public health at Bristol University and member of Independent Sage, also urged people to think about whether it was sensible to meet indoors and said there should be “no hugging”.

He added: “Can you meet outdoors, can you go out for a walk together? Can you do something else?

“If you are going to meet indoors, well then we’ve got a problem because a lot of our homes are not well ventilated these days.

“So what can you do you? You could open your windows … a through draft is absolutely perfect, it really reduces the spread.

“Wear masks indoors, if you’re really worried about it and you can’t keep apart.

“If you’re sitting around a table, well try and make that as big a space as you possibly can.”

Asked by Good Morning Britain presenter Piers Morgan if gatherings should be happening at all, TV medic Dr Hilary Jones said: “My gut feeling is it shouldn’t. It’s asking for trouble.

“It’s going to delay the vaccination programme because we will see an increased R (reproductive) rate come January and February almost inevitably, and that means that there will be people off sick who would be giving the vaccinations, people who can’t come to the vaccination centres because they’re already sick. It means that hospitals will be busier.

“And it will delay all the good things that we’re looking forward to now with vaccinations coming down the pipeline.”

However, Professor Paul Hunter, from the University of East Anglia, said gatherings are a “tolerable risk”, adding that shops and schools will be closed over the festive period and people will not be going to work, all driving down the R rate.

“It does carry with it a risk but, looking at the other side of things, January is generally a very bad month for people’s mental health,” he said.

“If being able to meet up in as safe a way as possible with your loved ones over Christmas gives you that extra strength to carry on until we’re able to get a lot more relaxed over spring, then I think that is a tolerable risk that I think we could accept.”

Boris Johnson’s official spokesman said: “There are no plans to review the Christmas guidance.

“What we’ve said alongside that is that the public should continue to be cautious.

“I think the Prime Minister said it’s the season to be jolly careful and we would emphasise that we should continue to do that.”