People are being warned not to gather in large groups over the Easter weekend, as Covid restrictions have been eased.
Britain's biggest police force has issued a warning that “house parties and dangerous raves” will be shut down.
While record-breaking sunshine at the start of the week saw large outdoor gatherings in parks and gardens across the country, police are concerned that colder weather over the weekend could drive people indoors.
Forecasters said a "big swing" in weather conditions could bring gale-force winds and even snow to parts of the UK over the bank holiday, while parts of the South would hang on to warmer conditions for the longest.
While groups of six, or two households, are allowed to meet outside, the Metropolitan Police said larger gatherings, including house parties and illegal raves, will be shut down.
Deputy Assistant Commissioner Jane Connors said: "We cannot allow the selfish actions of a small minority of people to jeopardise the efforts of this city.
"We will continue to shut down house parties or dangerous raves quickly, taking enforcement action by handing out fines.
"We make no apology for our tough stance on shutting down those large gatherings which pose a serious risk to public health."
The Met is expecting more protests in the capital over the weekend, which are now lawful providing organisers submit a risk assessment and take steps to ensure the gathering is safe.
But the force said: "Enforcement action will be taken, if needed, in the interests of public health."
Among the planned demonstrations is a Kill the Bill rally against the Government's proposed Police, Crime, Sentencing and Courts Bill due to take place in Finsbury Park on Friday afternoon, with similar events planned elsewhere.
Meanwhile, Greater Manchester Police sought to avoid a repeat of scenes played out across the country this week by introducing a 48-hour dispersal order for the city centre, to last until 3pm on Saturday.
It means officers can direct anyone acting anti-socially to leave the area.
What will the weather be like over Easter weekend?
Parts of the UK saw temperatures reach nearly 24C (75.2F) on Wednesday, with Weybourne, north Norfolk, leading the way at a peak of 23.9C (75F) - short of the nation's hottest ever March temperature of 25.6C (78F), which was recorded in 1968 at Mepal in Cambridgeshire.
But the Met Office said temperatures would decline steadily and by Monday would struggle to reach double digits due to the country entering an "Arctic trough".
Nicola Maxey, spokeswoman for the Met Office, said: "There are some blustery winds around, particularly along the east coast, as we go through the weekend.
"It's a marked change from what we saw on Wednesday and by the end of Friday we're really all in this cold air - we're in an Arctic trough."
Ms Maxey said that parts of the South would hang on to warmer temperatures for the longest but that by early next week the entire country would be in single figures.
On Saturday, temperatures in the South East and London are expected to be about 12C (53.6F) and, further north, Manchester and Leeds could see highs of 13C (55.4F) and 10C (50F) respectively.
But, by Monday, London may drop to 8C (46.4F), Manchester 7C (44.6F) and Leeds a chilly 5C (41F).