Temperatures rose more than 20 ° C in less than four hours as Britain entered a period of “exceptional warmth”.
Mercury rose to 19 ° C from a frosty minus 1.6 ° C at 7 a.m. in Santon Downham, west Suffolk, just before 11 a.m. on Tuesday, the Met Office said.
Photos show the heat drew crowds to Bournemouth beach in Dorset.
Temperatures in parts of south and east England are forecast to reach 23 ° C later in the day and rise to 24 ° C around London on Wednesday.
The figure comes close to the UK’s hottest March temperature of 25.6 ° C, recorded at Mepal in Cambridgeshire in 1968.
Should the temperatures exceed 23 ° C, this would be the first time since 2012 in March.
The Met Office tweeted that there would be “exceptional warmth” and “massive” temperature contrasts towards the end of the month.
Chief Meteorologist Steve Ramsdale said: “In the UK there will be a few days with particularly warm weather until the end of March, with a maximum of 24 ° C on Wednesdays in the south and east of England.
“There will also be plenty of sunshine in England and Wales, but parts of Scotland will have persistent rain for the next few days.
“Conditions will change as the day progresses on Thursday when cooler air flows in from the northeast. The highs fall into mid-teens before continuing to fall through Friday, particularly along the east coast.
“However, with the pressure building up from the north, conditions are expected to remain dry for the majority.”
Monday was the warmest day of the year so far for England and Northern Ireland with temperatures of 20.4 ° C and 17.3 ° C, respectively.
Mr Ramsdale said cold air will rush through the UK by Sunday, bringing with it a “remarkable” change in temperature and the chance of strong winds and wintry showers.