Covid-19 infections rose in England and Scotland earlier this month, while the trend in Wales and Northern Ireland was uncertain, figures show.
A total of 1.4 million people in private households in the UK are likely to have tested positive for coronavirus in the week to 9 December.
That was up from 1.1 million at the end of November, but down from the two million weekly infections at the start of October.
The estimates published by the Office for National Statistics (ONS) give a snapshot of what was happening in the UK at the beginning of December, when the coronavirus was starting to become more common among the population.
The latest figures show the number of people hospitalized with Covid-19 in England, Scotland and Wales is on a clear upward trend, with patients in England up 29% last week to the highest level for almost two months.
The ONS infection survey is the most reliable measure of the prevalence of the coronavirus and is based on a sample of household swab tests across the UK.
But there is a delay in reporting the data due to the time it takes to compile the survey.
Sarah Crofts, assistant director of infection survey analysis at the ONS, said: “Today’s data shows that Covid-19 infections have risen for the fourth consecutive week in England, with cases also continuing increasing in Scotland.
“More than half of English regions saw an increase, while it’s a mixed picture for different ages.
“Infections have increased among most adults under the age of 70, while high school-aged children experienced a decrease in infections.
“We will continue to monitor the data closely over the coming weeks.”