Professor Chris Whitty’s plea for people to consider cutting back socialising around Christmas due to the threat from the Omicron variant has prompted fresh calls for support to the hospitality sector.

Experts called for clearer messaging as Boris Johnson stopped short of matching England’s chief medical officer’s warning, instead urging people to “think carefully” before attending celebrations.

The variant was surging across the UK, with daily confirmed Covid-19 cases reaching a record high of 78,610 new cases and Prof Whitty warning “records will be broken a lot over the next few weeks”.

Businesses warned of a fresh threat hitting their existence as people weigh up whether to risk nights out or cancel to improve the chances of spending Christmas with their families.

One scientific adviser said it was possible one million people could be isolating on Christmas Day, with the 10-day isolation period for positive tests now covering December 25.

Prof Whitty told the public “don’t mix with people you don’t have to” at events that are not among the most important to them.

“I really think people should be prioritising those things – and only those things – that really matter to them,” he told a Downing Street press conference.

“Because otherwise the risk of someone getting infected at something that doesn’t really matter to them and then not being able to do the things that matter to them obviously goes up.”

The Prime Minister declined to go as far as Scotland’s First Minister Nicola Sturgeon, who has given specific guidance to urge people to limit their socialising to three households around Christmas.

“We’re not cancelling events, we’re not closing hospitality, we’re not cancelling people’s parties or their ability to mix,” he said.

“What we are saying is think carefully before you go. What kind of event is it? Are you likely to meet people who are vulnerable, are you going to meet loads of people you haven’t met before? And get a test.”

Chancellor Rishi Sunak, who was on a Government work trip to California, where he used to live, faced almost instantaneous calls for fresh support packages.

British Chambers of Commerce president Baroness Ruby McGregor-Smith said Prof Whitty’s call “will almost certainly have an enormous impact for businesses”.

“Despite this still we heard no news of any new financial support measures coming from Government to help those businesses, and others badly affected by the current restrictions,” she said.

Tory MP Anne Marie Morris added: “If we’re effectively telling people not to visit hospitality venues this Christmas, then this needs to be accompanied by immediate sector specific financial support from the Treasury.”

Theatre director Sir Nicholas Hytner said venues were in “crisis mode”, with shows closing as actors and other staff contracted coronavirus while bookings have “fallen off a cliff”.

The former artistic director of the National Theatre told BBC Newsnight: “We now surely don’t want to get into a situation where the Government’s investment last year is wasted because the sectors that it has supported collapse in the new year.

“We need to see short term finance, we need to see loans, we need to see VAT looked at again, we need to see business rates looked at again.”

On the same show, renowned chef Tom Kerridge called for a return of the drop of VAT to 5% for the hospitality industry, adding: “Undoubtedly there will be many places that close their doors for Christmas and don’t reopen.”

The Treasury insisted some support packages remain in place and said it will “continue to respond proportionately to the changing path of the virus”, but set out no new measures.

A spokeswoman added: “The Chancellor is in the US on a long-planned trip conducting Government business.”

Professor Sir David Spiegelhalter, who advises the Government on the Scientific Advisory Group for Emergencies (Sage), said it is possible that a million people could be isolating with Covid infections on Christmas Day.

The Cambridge University academic told BBC Newsnight: “I haven’t seen the sums behind it, it sounds like it is in fact possible.

“It depends on whether people get tested, because more than half of people who are infected don’t go on and get tested. But we do know there is going to be huge disruption.”

Professor Stephen Reicher, who is on the Scientific Pandemic Insights Group on Behaviours (Spi-B), said Mr Johnson declining to be as explicit as Prof Whitty was “deeply problematic”.

“He couldn’t say don’t go to nightclubs if you want to meet your loved ones at Christmas, and I think that leads to mixed messaging which is really problematic,” he told Channel 4 News.

“Because the clear message that needs to go out to everybody is yes get your booster, that will work in a few weeks’ time, but now to stop the new variant taking over be cautious, be careful, don’t socialise unless you have to.”

Sage’s Professor Andrew Hayward also called for “clearer messaging” about people reducing their social contacts.

The University College London academic told Newsnight: “By the time we know all the answers we want to know about severity it might be too late to do much about it, which I think is why it does make sense for people to be really quite cautious and I would personally like to see clearer messaging about people reducing their social contacts.

“That idea that if you want to go home for Christmas try not to catch Covid in the next few days is a very sensible one.”