The UK has recorded its highest March temperature in 53 years after the mercury hit 24.2C (75.5F).
The record was broken in St James’s Park, central London, this afternoon, according to the Met Office.
It is the highest March temperature since 1968, when the heat reached 25.6C (78F) in Mepal, Cambridgeshire.
Temperatures increased by more than 20C in less than four hours in Santon Downham, west Suffolk, earlier today.
The village went from just 1.6C (34.9F) at 7am to 19C (66.2F) shortly before 11am.
Britain is expected to experience more unusually-warm spring weather on Wednesday, when temperatures could reach 25C (77C) in London and the South East.
But after thousands flocked to beaches and parks nationwide as lockdown eased in England, police forces up and down the country have urged people to stick to the COVID rules.
Met Police tweeted: "Easing of lockdown. Let’s take this next step safely."
At a Downing Street news briefing yesterday, Prime Minister Boris Johnson issued a similar warning.
He said hoped Britons would take advantage of the "beautiful weather" to play sport or exercise but urged people to "proceed with caution".
"I know how much government has asked of the people in the last year, but I also know how magnificently – incredible patience and fortitude – people have responded," he said.
"That’s why I stress the importance of everybody maintaining the discipline people have shown for so long."
People flocked to The Arboretum on Monday with beer crates, barbecues and loud speakers, with reports of some climbing trees and fighting.
Assistant chief constable of Nottinghamshire Police, Steve Cooper, described the scenes as "disappointing and irresponsible".
ACC Cooper said his force had been "caught by surprise", but they will now strengthen their policing as a result.
He said: "The behaviour yesterday was unacceptable and we are disappointed people decided to behave in this selfish way.
"That is why we have now taken the decision to put a dispersal order in place."
The good weather will continue through to Thursday, forecasters say, but will be replaced by a cooler spell over the Easter Bank Holiday weekend.
Met Office chief meteorologist Steve Ramsdale said: "Conditions will start to change through the day on Thursday as cooler air moves in from the north east, highs will fall to the mid-teens before falling further by Friday, especially along the east coast.
"With pressure building from the north however, conditions are expected to remain dry for the majority."