LONDON, Dec 15 (Reuters) - England"s chief medical officer warned people not to mix with others unless they have to in the run-up to Christmas after Britain recorded its most daily coronavirus cases since the start of the pandemic. With a new highly transmissible Omicron variant of the virus surging across Britain, a further 78,610 COVID-19 infections were reported on Wednesday, about 10,000 more than the previous high reported in January. Chief Medical Officer Chris Whitty said that Britain is being hit by "two epidemics on top of each other" as he urged the public to scale back their Christmas plans. "People should be prioritising those things, and only those things, that really matter to them," he told a news conference. "Don"t mix with people you don"t have to." Whitty warned that the number of daily cases would continue to break records in the next few weeks and a big rise in hospitalisations is "a nailed-on prospect". Prime Minister Boris Johnson agreed with a "general instinct to be more cautious" but ruled out further government restrictions for now. "We"re not cancelling events, we"re not closing hospitality, we"re not cancelling people"s parties or their ability to mix," he said. More than 11 million people have now tested positive for the disease in the United Kingdom, which has a total population of around 67 million. While the number of daily cases is at a record, deaths are running at a much lower level than earlier in the pandemic. The government hope that a rapid booster rollout will help keep levels of severe disease low even as cases rise. People wait in a queue to get a dose of the COVID-19 booster vaccine, amid the coronavirus disease (COVID-19) pandemic, at Smallthorne Community Centre in Stoke-on-Trent, Britain, December 15, 2021. REUTERS/Carl Recine People queue at a coronavirus disease (COVID-19) vaccination centre in London, Britain, December 15, 2021. REUTERS/Hannah McKay A woman reacts as she receives a dose of a COVID-19 vaccine at a coronavirus disease (COVID-19) vaccination centre in London, Britain, December 15, 2021. REUTERS/Hannah McKay 1/3 People queue at a coronavirus disease (COVID-19) vaccination centre in London, Britain, December 15, 2021. REUTERS/Hannah McKay THREAT TO HEALTH SERVICE Jenny Harries, chief executive of the UK Health Security Agency, earlier called the Omicron variant "probably the most significant threat" since the start of the pandemic. "The numbers that we see on data over the next few days will be quite staggering compared to the rate of growth that we"ve seen in cases for previous variants," she told a parliamentary committee. Harries said that Omicron had the potential to put the national health service "in serious peril" because of the speed at which infections were increasing. Amanda Pritchard, head of the National Health Service in England, told lawmakers that the health service was now gearing up for a wave of hospitalisations "as big or even bigger than the previous wave this time last year". She said that the record tally "should worry all of us". The new variant of the virus has a doubling time under two days in most regions in Britain, with its growth rate was being notable in London and Manchester in particular. More than 10,000 cases of Omicron have been recorded, with at least 10 people hospitalised. One person has died after contracting the variant, which is set to become the dominant strain in London. More than 146,000 people have died from COVID-19 in the United Kingdom.