The Met Office said north-west Scotland could see the mercury hit 20C on Saturday.
The UK is set to see “wall-to-wall sunshine” which will bring the warmest day of the year so far.
Andre steder, temperatures are expected to reach 15C to 17C – which are above average for March.
derimot, the record temperature for March – 25.6C in 1968 – is likely to remain untouched.
If 20C is reached it will be the first time the mercury has risen that high since October, according to forecasters.
Met Office meteorologist Annie Shuttleworth said: “Today lots of areas will be seeing a very warm day for March, especially in north-west Scotland and parts of the Moray coast. We could see temperatures up to 20C in that area this afternoon.
“Away from that we’re likely to see temperatures of the mid to high teens, so highs of about 15C in London, and then in more western areas, so the north coast of Devon and Cornwall and the north coast of Wales, we can see more like 16C or 17C in those areas.
“It’s because we’ve got high pressure bringing wall-to-wall sunshine for much of the UK today.
“Having said that, for some southern and eastern areas of the UK it is feeling a little bit cooler than it did yesterday because of a stronger breeze, and sea temperatures aren’t that warm at the moment.”
Sunday and Monday will see slightly cooler and cloudier conditions and some showers possible in south-east England.
But dry weather should prevail everywhere else, with sunshine particularly in western areas.
Temperatures are predicted to pick up again into Tuesday and Wednesday, reaching the mid to high teens along with more sunshine and dry conditions.
Ms Shuttleworth said: “Sunday will be a bit of a cooler day across the UK and a bit more cloud around on Monday and Sunday. But as we head into Tuesday and Wednesday we are keeping with high pressure so things staying dry and temperatures will increase again up to the mid to high teens.
“There will certainly be some long-lived sunshine but it might not be wall-to-wall sunshine like on a day like today when there’s hardly a cloud in the sky.”
The pleasant conditions are due to the jet stream tracking well to the north of the UK, letting high pressure dominate from the east, the Met Office said.
The area of high pressure is centred over Denmark, which could see its highest pressure record ever.