Watch: People enjoy the warm weather on Bournemouth beach
Temperatures peaked at 24.5C (76.1F) at Kew Gardens in west London on Tuesday, making it the hottest day of the year, the second warmest March day on record and the hottest March day in 53 years, according to the Met Office.
The rules on social gatherings eased this week, with the rule of six brought back – but only if people are meeting outside.
As a result, outdoor spaces were packed with people, including at Brighton beach, where fire jugglers performed for crowds.
However, the sight of thousands of people flocking together just as the regulations eased prompted police to urge sun-seekers to stay away from large public spaces over fears COVID numbers could start to rise.
Nottinghamshire Police issued a dispersal order after large crowds gathered at Nottingham Arboretum, with some appearing to flout rules on social distancing.
Assistant chief constable Steve Cooper said: “While we can of course understand people’s desire to want to be out in the sun and enjoying these mild temperatures we are currently experiencing, the government and our health colleagues remain extremely cautious and advise that people continue to minimise social contact.
“We would like to remind people that we are still only partly out of lockdown measures.
“This week has seen the easing of some of the restrictions but we are still required to keep our distance from each other and only mix with one other household outdoors, up to six people.”
After a brawl broke out in the city park, alcohol was also banned from anyone attempting to enter.
Councillor David Mellen from Nottingham City Council added: “Over 600 local people have died due to the virus.
“We owe it to their families, to each other and to frontline workers not to jeopardise the strides we have made towards reducing the spread of COVID by acting so thoughtlessly and recklessly.”
Meanwhile, a beach bar was ordered to stop selling alcohol after customers queued for 40 minutes for a pint.
The Beach Bar on Cleethorpes Promenade, Lincs, opened up to customers on Monday, even though pubs remain closed for lockdown.
North East Lincolnshire licensing officers have now served a notice on the premises, ordering it to stop selling alcohol.
But owner Kash Pungi claims his business is exempt and said he was not given a chance to explain when the regulation was served on him.
He says he was operating a click and collect service where customers pre-order with a text message and insists he was following regulations after taking advice from a leading licensing consultant.
He told Grimsby Live :"They are making it harder for businesses in Cleethorpes that are just trying to provide a service. I have always worked with the council but this is making it harder."
A spokesman from North East Lincolnshire Council said officers “took legal advice” before serving the prohibition notice.
In Leeds, crowds were also out to enjoy the sunshine at Woodhouse Moor in Hyde Park.
One resident who lives in viewing distance of Woodhouse Moor said: "I hope there's no outbreak, but they can't exactly be upset if there is one. It's selfish on their part, but understandable.”
Another resident said there were “literally hundreds” of people at the park, many having barbecues in the March heat.
Following the scenes of crowds gathering, health secretary Matt Hancock said that while people enjoy the sun, they need to be careful not to “blow it” at this stage of the coronavirus pandemic.
He tweeted: “Let’s enjoy the sun but let’s do it safely. We have come so far, don’t blow it now.”
Despite the concerns, a leading government adviser has previously stated that there has “never” been a COVID outbreak linked to a crowded beach.
Last month, Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh and an adviser to the government's Sage advisory group, told the Commons science committee that beaches are not a hotbed for coronavirus transmission.
Asked about the risk of transmission in outdoor activities, he said: “Mass gatherings are absolutely a special case. Even outdoors they don't involve social distancing so those are clearly higher-risk than normal outdoor activities.
“But, for example, over the summer we were treated to all this on the television, news, pictures of crowded beaches and there was an outcry over this.
“There were no outbreaks linked to crowded beaches. There has never been a COVID-19 outbreak linked to a beach ever anywhere in the world to the best of my knowledge.”
Tuesday’s peak temperature was only slightly below the UK’s hottest ever March temperature of 25.6C (78F), recorded in 1968 at Mepal in Cambridgeshire.
However, Met Office forecaster Alex Burkill said it was a “possibility” that the record could be broken on Wednesday, with temperatures expected to reach around 25C (77F).
Watch: How England will leave lockdown