Forecasters have said there is a 10% chance the UK could bask in the hottest March day on record on Wednesday.
Parts of London and the South East will be warmer than Benidorm, Marbella and Tenerife by midday as the early spring heatwave continues.
But politicians have warned people to remain “cautious” while visiting parks and beaches after large crowds were seen gathering in public spaces in warm weather on Tuesday.
The nation’s hottest ever March temperature of 25.6C (78F) was recorded in 1968 at Mepal in Cambridgeshire and the Met Office said the mercury is expected to rise to similar levels on Wednesday.
Met Office spokesman Grahame Madge told the PA news agency: “There is a chance we could see our hottest March day on record today, we’re predicting a 10% chance that it could happen.
“There are a number of factors that may stop that happening, as it will be rather cloudy in places, which could develop into shower clouds, taking the heat away.
“But certainly it should be warmer than yesterday in some areas.”
Mr Madge said temperatures of 24.7C (76.5F) are expected in London and the South East, while parts of central and eastern England and Wales should be around 20C-22C (68F-71.6F).
The mercury peaked at 24.5C (76.1F) at Kew Gardens in west London on Tuesday, with St James’s Park in the centre of the capital hitting highs of 24.3C (75.7F).
People made the most of the sunny conditions after Monday’s easing of coronavirus rules, which means groups of up to six, or two households, are now able to socialise in parks and gardens and that outdoor sports facilities can reopen.
Adam Jones, from Moseley, Birmingham, said he saw a “couple of thousand” people convened in Cannon Hill Park, to the south of the city, while out walking with his girlfriend on Tuesday evening.
“It has been noticeably busier since restrictions eased but yesterday was really busy,” the 27-year-old said.
“While there were a fair few people in small groups respecting distancing, they were overshadowed by lots of big groups, sometimes up to 20 to 25 people, blaring music.
“We did one lap of the park and by the time we were leaving it looked like a festival.
“How it looked this morning was disgraceful – so much rubbish that a council worker estimated it would take the whole team most of the day to clear.”
Superintendent Farooq Sheikh, of Birmingham East police, said: “We had officers at Cannon Hill Park yesterday following social posts suggesting that an organised gathering was planned.
“Officers initially found no breaches of coronavirus legislation, with people enjoying the weather in small, individual groups.
“Later on in the evening, the numbers increased and music and lighting equipment had been set up. We had a number of complaints from residents about traffic building up around the area.
“The crowds were good-natured and engaged with officers, and the park was all clear by 11.30pm.
“Officers did not need to issue any fines.
“We will have extra police officers in the area today, who will be able to use our powers to quickly break up any gatherings that put people’s health at risk.
“We want to reinforce that it is really important to remember that, while people can now meet up with five other people outside, large-scale organised events are still against the law.”
A 14-year-old boy died after getting into difficulties at Goit Stock waterfall in Cullingworth, West Yorkshire, on Tuesday evening, West Yorkshire Police said.
Officers have asked for a group of males who tried to help to come forward so they can piece together what happened.
The force said on Wednesday: “Emergency services were called just after 6pm yesterday evening to reports of a concern for safety.
“A 14-year-old male had entered the water and got into difficulty.
“Emergency services attended, including fire service, ambulance and underwater rescue teams, and recovered a body from the water.
“Police are appealing for witnesses of the incident and in particular, there was a group of males in the area who tried to help the teenager and police would urge them or anyone in the area to come forward and assist with the circumstances of the incident.”
Communities Secretary Robert Jenrick urged people to enjoy the sunshine in a “sensible, cautious” manner by sticking to the rules.
He told ITV’s Good Morning Britain: “We just need to exercise caution and be sensible and pragmatic about how we do that.
“I think the vast majority of people are and will do that, they will enjoy the sunshine this week and at the Easter weekend, but they’ll do so in a sensible, cautious way.
“The two things aren’t mutually exclusive – you can go and out, have fun, enjoy the great outdoors and the sunshine, while also trying to be careful, sticking to the rules and trying to avoid the most crowded places.”
Health Secretary Matt Hancock also tweeted, saying: “Let’s enjoy the sun but let’s do it safely. We have come so far, don’t blow it now.”
However, parts of Northern Ireland and Scotland will remain cloudy and wet, with temperatures barely hitting the mid-teens, Mr Madge said.
Temperatures will then drop to the low teens in the east of England from Thursday.
Mr Madge said a “cold front” will start moving down from the north, bringing with it colder, windier conditions in stark contrast to the previous “warm southerly winds”.
Wet weather is forecast for Easter Sunday, with the chance of sleet or snow in Scotland and the far north of England.
Mr Madge added: “Friday should mark a rather malign start to Easter, with colder conditions for large swathes of the country as part of an Arctic plunge.
“Temperatures will be dragged down quite a bit from the day before, with wintry showers expected in Scotland and the most northern regions in England.”