A warm spell could enable the UK to break its record March temperature of 25.6C (78F) next week.
A southerly air flow will bring conditions similar to those in southwest France and southern Spain on Monday and Tuesday.
Temperatures are forecast to get very close to the record figure, set in Mepal, Cambridgeshire, in 1968.
London is most likely to see such unseasonal March conditions, along with areas just north of the capital.
The warmth will be relatively widespread, however, with temperatures reaching the early 20s Celsius for many parts of England and Wales.
And although parts of the north will be wet, temperatures will be higher than average there too.
That will especially be the case on Monday for eastern parts of Scotland, where temperatures could locally be up into the upper teens.
Met Office forecaster, Greg Dewhurst, said: "Into next week, large swathes of southern England and Wales will be dry with warmer temperatures than expected for this time of year, the average for March being 11 (51.8F) to 12C (53F).
"The mercury could reach a high of around 18C (64.4F) on Monday, with Tuesday seeing highs of 24C (75.2F).
"Much of the UK will remain dry and bright until Wednesday, while parts of Scotland will see some heavy showers."
Average maximum temperatures for the end of March in the UK and Ireland are around 12C (53F) in the south and 8C (46F) in the north.
The Easter weekend is looking much chillier, however, as a significantly colder air mass is due to sweep southwards mid-week.
While the holiday weekend is looking mostly fine and settled thanks to high pressure, some places will experience wintry showers.
This coming weekend will also be disappointing for some, with blustery showers turning increasingly wintry.
Mr Dewhurst said: "The weekend should be a mixed bag for many with a big north-south split.
"Southern regions will certainly see the warmer, sunnier conditions with a band of rain moving through Northern Ireland on Saturday afternoon before heading into parts of northern England and Scotland.
"Saturday will certainly be the better of the two days, with Sunday becoming windy and grey for most."