Temperatures increased by more than 20C in less than four hours as the UK entered a period of “exceptional warmth”.
The mercury climbed from a frosty minus 1.6C at 7am in Santon Downham, west Suffolk, to 19C shortly before 11am on Tuesday, the Met Office said.
Temperatures are forecast to hit 23C in parts of south and east England later in the day, rising to 24C on Wednesday around London.
The figure comes close to the UK’s hottest March temperature of 25.6C, recorded in 1968 at Mepal in Cambridgeshire.
Should temperatures exceed 23C, it would be the first time in March since 2012.
The Met Office tweeted there would be “some exceptional warmth” and “massive” temperature contrasts as the month comes to a close.
Chief meteorologist Steve Ramsdale said: “The UK will see a few days of notably warm weather to end March, with a maximum of 24C on Wednesday in the south and east of England.
“There will also be plenty of sunshine across England and Wales, however parts of Scotland will see some persistent rain over the next couple of days.
“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.”
Monday was the warmest day of the year so far for England and Northern Ireland, with temperatures hitting 20.4C and 17.3C respectively.
Mr Ramsdale said cold air will push across the UK through Sunday, bringing a “notable” change in temperature and the chance of strong wind and wintry showers.