The highest Covid death toll since April and the discovery of a second new variant of the virus have led to stark warnings that ministers are acting too slowly by waiting until Boxing Day to put 6 million more people into the toughest restrictions. A swathe of England will be placed under lockdown-like tier 4 curbs from Saturday, the health secretary, Matt Hancock, announced as the UK recorded 744 deaths – the highest since late April – and 39,237 cases. In total, 42% of England – nearly 24 million people – will be in tier 4 with a further 44% (nearly 25 million) in tier 3. With the virus surging 57% across the country in a week, and the R number rising to 1-1.3, the Isles of Scilly are the only area remaining in tier 1. The introduction of new measures on Boxing Day will leave millions of people in the worst-affected areas free to mix indoors with up to three households on Christmas Day when restrictions are eased for 24 hours. One expert warned the delay of “critical days” will mean “case numbers are going to be much, much higher” and “much more difficult to bring down”. Wales, Scotland and Northern Ireland have announced nationwide restrictions in recent days in an attempt to contain the new variant announced last week, which emerged in Kent and is said to be up to 70% more infectious. On Wednesday, Northern Ireland’s Department of Health confirmed a positive test in the region for the new variant of Covid-19 that was first detected in Great Britain. During a Downing Street press conference on Wednesday to unveil the new tier moves, Hancock revealed details of a second Covid variant linked to South Africa that had been found in the UK. Late on Wednesday, the UK government announced that visitors from South Africa, or those who have passed through the country in the last 10 days, would be barred from entering England from 9am on Christmas Eve and direct flights would be banned. The ban excludes cargo and freight without passengers and also does not include British and Irish nationals, visa holders and permanent residents, who can still enter but must self-isolate along with their household for 10 days. Hancock also said coronavirus cases had risen 57% across the country in the last week, with nearly 19,000 in hospital with the virus. Hancock added: “Against this backdrop of rising infections, rising hospitalisations and rising numbers of people dying from coronavirus it is absolutely vital that we act. We simply cannot have the kind of Christmas that we all yearn for.” He also said: “We know that the three-tiered system worked to control the old variant and is working now in large parts of the country, especially in northern England. But we also know that tier 3 is not enough to control the new variant. This is not a hypothesis, it is a fact and we’ve seen it on the ground.” Dr Andrew Preston, reader in microbial pathogenesis at the University of Bath, said: “The situation is fast-moving and requires decisive decision-making. Today, the government has recognised that the situation is continuing to deteriorate in many areas and that tougher restrictions are required if the hope is to contain it. “With cases rising so quickly, the delay of three critical days – with new tiering not taking effect until Boxing Day – will mean that by then case numbers are going to be much, much higher and as a result much, much more difficult to bring down. If containment is the focus, then unfortunately, the restrictions need to be immediate, despite the fallout this will cause.” Before the announcement, Christina Pagel, professor of operational research at University College London, said waiting until Boxing Day to put more areas into tier 4 was too slow. She told Times Radio: “We are in an incredibly dangerous situation … If we just wait and we let it spread to the north, where things are much more under control, then the whole country is on fire and I just feel like we have to stop it now and protect the north from the south, effectively.” She added: “We’re constantly behind the curve. I think we have to put the whole country in tier 4 today, especially in those tier 2 areas around tier 4 that are just going through the roof. Why are we letting people mix at Christmas? You are just asking for trouble.”