The government revealed 49,156 new cases of Covid-19 on Monday, the highest since July 17.
Cases are up over 16% in the past seven days.
Downing Street acknowledged that winter would be “challenging” when questioned about rising coronavirus rates.
The prime minister’s official spokesman said: “We obviously keep very close watch on the latest statistics.
“We always knew the coming months would be challenging."
They said the government would be keeping a "close eye" on cases.
The government also said a further 45 people had died within 28 days of testing positive for Covid-19 as of Monday, bringing the UK total to 138,629.
Separate figures published by the Office for National Statistics show there have been 163,000 deaths registered in the UK where Covid-19 was mentioned on the death certificate.
England reported 22 new deaths from Covid-19 on Monday and 39,473 new cases.
Wales reported a further 6,398 new cases from Covid-19 on Monday and 20 more deaths.
Scotland had 2,194 new cases of Covid-19 on Monday but no new deaths.
Northern Ireland reported 3 new deaths from Covid-19 and 1,091 new cases on Monday.
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