In Scotland, there were an additional 265 omicron cases, pushing the total to 561, while in Wales the figure nearly doubled, to 62, and in Northern Ireland the figure shot up by 139, to 151.
The UK recorded a further 78,610 cases of coronavirus on Wednesday, government figures show, making it the worst day for infections since the pandemic began in March 2020.
That is more than 10,000 cases higher than the previous record daily infection rate, which came during the peak last winter when there were 68,053 infections reported on 8 January.
The same data released on Wednesday afternoon showed an additional 165 people died within 28 days of testing positive for Covid-19.
Experts said the figures demonstrate how vaccines have been providing strong protection against death, as on 8 January there were 985 deaths reported.
Of the new infections, 4,237 additional omicron cases were reported across England, taking the total number of confirmed cases of the new variant in England to 9,243.
Across the four nations as a whole, the UK Health Security Agency said a further 4,671 confirmed cases of the omicron variant had been reported, bringing the total to 10,017.
Regarding vaccine uptake, the figures showed a further 34,082 first doses had been administered, 37,888 second doses and 656,711 booster and third doses. Separate totals for booster and third doses are not available.
Commenting on the surging cases, Amanda Pritchard, chief executive of NHS England, said the latest daily total “should worry all of us”.
She told the Commons Public Accounts Committee: “That is a stark reminder of why the current national mission to get Covid vaccination is the right one.
“I think that figure should worry all of us and that’s why the booster programme is so important.”
The data followed a warning from a leading scientist about the possibility the NHS could be overwhelmed next month amid uncertainties over the impact of omicron.
Professor Graham Medley, from the London School of Hygiene & Tropical Medicine and a member of the Scientific Advisory Group for Emergencies (Sage), told BBC Radio 4’s Today programme he was worried “we could see numbers of people being admitted to hospital getting very large” if infections continue to rise and spill into older age groups.
Prof Medley said there is not currently any good information on the severity of omicron but added: “We are a population in a very different position to this time last year, in the sense that the majority of people have been vaccinated and there has been much infection since then, so there is much more immunity…
“The fact that we are much more immune than we were generally means that the virus will appear to be much less severe.
“So, individually, we have a much lower risk but the numbers of infections means that even though individually we’re at less risk, at a population level (the) number of people ending up in hospital could get very large.”
Asked if hospitals could end up overwhelmed, he said: “I think that that is a very real possibility.
“If the numbers of infections increasing continues in the way that it has done, and it spills out into older age groups, then we could see numbers of people being admitted to hospital getting very large and certainly going over the 1,000, maybe up to 2,000 a day, that we’ve managed to keep the delta variant below.”
It came as Dr Jenny Harries, chief executive of the UK Health Security Agency, told MPs the omicron variant is “probably the most significant threat we’ve had since the start of the pandemic” and warned of a “staggering” number of cases in the next few days compared with what has gone before.
She said the “real potential risk” is whether “cases turn into severe disease, hospitalisations and deaths”, but added that it is “too early” to be clear on that.
