Temperatures in parts of the South East are expected to be significantly warmer this week as families and friends are reunited and sporting activities are allowed to resume in England.
Some areas may see highs of 19C on Monday afternoon with a possible peak of 24C on Wednesday, the Met Office said.
The warm weather coincides with a major easing of England’s lockdown measures, when the “stay at home” order will end, and groups of six people, or two households, can meet outside.
Outdoor sporting venues such as football and cricket pitches, tennis and basketball courts, outdoor swimming pools, golf courses and sailing clubs will also be allowed to reopen.
Forecasters said the best of the weather is expected on Wednesday, with sunny spells “persisting” and a high of 24C in London and the South of England.
Met Office spokesman Oli Claydon said clouds will also “start to thin” and give way to clear skies and sunshine for much of the week.
Temperatures in March have not gone above 24C since March 29 1968, when 25.6C was recorded in Mepal in Cambridgeshire.
Mr Claydon said: “On Monday we could see highs of 19C in parts of eastern England, near Humberside and East Anglia, and warm quite widely.
“Looking ahead to Tuesday, 23C is likely to be the maximum in parts of of south-eastern England.
“Wednesday is the headline figure for the week with our highest temperature of 24C, and here we’re looking at London…”
But Mr Claydon warned that, by the Easter weekend, cold air from the north may bring a “notable” dip in temperatures, with showers forecast to spread to most areas.
“We’ve got a cold front moving through so that will knock temperatures down, and by Friday we’re going to be back into mid-single figures, so quite a notable change by the end of the week,” he said.
The Met said temperatures are likely to be around or below average for the time of the year, with a potential for widespread overnight frosts.