Omicron could cause between 25,000 and 75,000 deaths in England over the next five months without tougher Covid restrictions, experts have told the government.

Scientists from the London School of Hygiene and Tropical Medicine (LSHTM) also warned that Omicron, first discovered in southern Africa, is likely to be the dominant coronavirus variant by the end of the month.

Even in the most optimistic scenario, projected infections could lead to a peak of more than 2,000 daily hospital admissions, with a total of 175,000 hospital admissions and 24,700 deaths between 1 December and 30 April.

The scientists, who advise the government as part of the Scientific Advisory Group for Emergencies (Sage) and the Scientific Pandemic Influenza Group on Modelling (Spi-M), used experimental data to look at how the transmission of Omicron might develop as the country heads into 2022 without more stringent restrictions beyond Boris Johnson’s “plan B”.

Another 633 Omicron cases were recorded in the UK on Saturday, marking the largest daily increase since the variant was detected. It brings the total number of confirmed Omicron cases to 1,898, according to the UK Health Security Agency. Overall, a further 54,073 new Covid cases were reported on Saturday with 132 deaths.

Dr Nick Davies, from LSHTM’s Centre for Mathematical Modelling of Infectious Diseases, who co-led the research, said on Saturday: “These are early estimates, but they do suggest that, overall, Omicron is outcompeting Delta rapidly by evading vaccines to a substantial degree.

“If current trends continue, then Omicron may represent half of UK cases by the end of December.”

They also found that booster jabs provided additional protection against Omicron, with a higher uptake likely to reduce the number of infections, hospital admissions and deaths.

Bringing in additional control measures early next year beyond plan B, such as restrictions on indoor hospitality, the closure of some entertainment venues and restrictions on how many people can gather in one place, would reduce hospital admissions by 53,000 and deaths by 7,600, scientists predict.

Dr Rosanna Barnard from LSHTM’s Centre for the Mathematical Modelling of Infectious Diseases, added: “In our most optimistic scenario, the impact of Omicron in the early part of 2022 would be reduced with mild control measures such as working from home.

“However, our most pessimistic scenario suggests that we may have to endure more stringent restrictions to ensure the NHS is not overwhelmed. Mask-wearing, social distancing and booster jabs are vital, but may not be enough.

“Nobody wants to endure another lockdown, but last-resort measures may be required to protect health services if Omicron has a significant level of immune escape or otherwise increased transmissibility compared to Delta.”

However, Prof Paul Hunter, of the University of East Anglia, said any model was “only as good as its assumptions”, adding that one key assumption here was that severity of disease outcomes for Omicron was the same as for Delta.

“Although we will not know for certain for a few weeks, indications from South Africa do suggest that Omicron does cause less severe disease than Delta,” he said.

He added: “If Omicron is indeed associated with less severe disease – as is, in my view, likely to be the case – then these models would overestimate hospital admissions and deaths, possibly substantially.

“As better data becomes available in the coming weeks, we can expect these models to be refined.”

Prof Eleanor Riley, from the University of Edinburgh, said earlier on Saturday that Omicron was spreading so fast that people were “very likely” to meet someone infected with the Covid variant unless they were “living the life of a hermit”.

Riley also warned that “a lot of people” could still end up in hospital even if Omicron is found to provoke milder symptoms than the Delta variant.

Riley told BBC Radio 4’s Today programme: “Omicron is spreading so quickly that, I think, unless you are living the life of a hermit, you are very likely to come across it in the next few weeks.

“I don’t think anyone should be going around thinking they are not going to catch it. I think that situation has changed.”

A spokesperson for the government said it continued to look closely at all of the emerging data, adding: “Plan B remains a proportionate response based upon what we know, so we encourage everyone to follow the rules by wearing a face covering, working from home if you can, testing regularly and coming forward for your booster when called.”