Christmas will go ahead without any curbs on socialising, Boris Johnson has confirmed, prompting warnings this could lead to tougher measures later despite tentative signs that cases have begun to plateau. The prime minister said he understood that families across England needed certainty to press ahead with Christmas plans but warned curbs could still be imposed after 25 December because of the rapid spread of the Omicron variant. From today, the Covid self-isolation period in England will be cut from 10 days to seven for vaccinated and unvaccinated people in a move that could also help save Christmas for tens of thousands of people if they get the all-clear from lateral flow tests on days six and seven, the government announced. However, those who are not fully vaccinated will still have to isolate for the full 10 days if they are a close contact of someone who has tested positive. The Christmas decision, which follows deep splits within the cabinet, was in contrast to moves by the Scottish and Welsh governments on Tuesday. Scotland cancelled Hogmanay street parties for tens of thousands of people, Wales announced £60 fines for employees who refuse to work from home, and both countries said sporting events would be held behind closed doors. Nicola Sturgeon had previously urged indoor mixing to be limited to three households either side of Christmas Day. Labour said that while the news about Christmas in England would be a relief to many, Johnson now appeared to be “too weak” to push any new restrictions through his cabinet if they were needed. The number of reported Covid cases across the UK fell for the third time in five days on Tuesday, raising hopes the recent surge may be starting to plateau – albeit at record high levels. There were 90,629 confirmed cases on Tuesday compared with a high of 93,045 on Friday. Paul Hunter, professor in medicine at the University of East Anglia, said that the recent rapid increase had slowed and numbers may now have “plateaued”. “I was pretty fed up last Thursday, but I am more optimistic tonight,” he said. “Even with all the caveats and sources of bias that might be influencing … it does give me hope.” Hunter said factors such as fewer people wishing to be tested in case it rules out Christmas gatherings with family could be at play – but none could sufficiently explain the trend of the last five days. “Looking at the rate of growth from two weeks ago, if that had continued we would have been expecting to report today something in excess of 200,000 [confirmed cases], rather than the 90,000,” he said. While he didn’t believe infections were falling, they could be stabilising, he said. “At the moment, the data looks as if it has plateaued. But there are caveats to that, that mean we still have to be somewhat cautious.” Hospitalisations are rising slightly but “the jury is still out” on whether the NHS could be overwhelmed next month, he added. In a brief video clip, Johnson said the situation with Omicron – which is highly transmissible and less responsive to vaccines – “remains extremely difficult but I also recognise that people have been waiting to hear whether their Christmas plans are going to be affected”. “So what I can say tonight is that naturally we can’t rule out any further measures after Christmas – and we’re going to keep a constant eye on the data, and we’ll do whatever it takes to protect public health. “But in view of the continuing uncertainty about several things – the severity of Omicron, uncertainty about the hospitalisation rate or the impact of the vaccine rollout or the boosters, we don’t think today that there is enough evidence to justify any tougher measures before Christmas.” He did not rule out post-Christmas curbs being announced this week but unless the data moves quickly that now seems unlikely. It is understood that any post-Christmas measures would involve regulations, requiring a vote in parliament, rather than just a change to advice. While Johnson reiterated warnings that people should be careful about Christmas plans, particularly with vulnerable relatives, some scientists said the lack of new rules carried significant risk. “This is a very risky approach and is very likely to result in the need for more stringent restrictions in the near future,” said Prof Lawrence Young, a virologist and professor of molecular oncology at the University of Warwick. “Waiting for case numbers and hospitalisations to increase is likely to be too late to suppress the spread of the Omicron variant and will subject the NHS to unprecedented pressure. A short circuit break now would have prevented more people from getting infected and from having to isolate which is now impacting many essential services.” Johnson’s announcement came after a long and divisive meeting of his top team on Monday during which the chancellor, Rishi Sunak, the foreign secretary, Liz Truss, and the education secretary, Nadhim Zahawi, are understood to have warned against new measures. All have been linked with potential bids to become the next Conservative party leader, in particular following a rebellion by 100 Tory MPs over Covid curbs and a historic byelection defeat last week. Wes Streeting, the shadow health secretary, said: “Boris Johnson is too weak to get any measures to keep the country safe through his cabinet. The prime minister is focused on clinging on to his job, half his cabinet are preparing their leadership campaigns, and the country is left with no plan to deal with the imminent threat of Omicron. The government must stop arguing amongst itself, come forward with a plan, and give people and businesses clarity.” • This article was amended on 22 December 2021. After publication the UKHSA clarified that the seven-day period also applied to unvaccinated people who tested negative on days six and seven, although the 10-day period would still apply to those who were not fully vaccinated if they were a close contact of someone who had tested positive.