The UK is expected to have its hottest day of the year so far on Friday as temperatures could reach 23C (73F) in some areas.
The warmest weather is expected to be in the west of London out towards Oxfordshire and the south Midlands, and could be hotter than Marbella and Ibiza in Spain.
Cardiff in Wales could see the mercury rise to 21C, while Scotland and Northern Ireland are set to be cooler - around 10C in Edinburgh and 15C in Belfast.
Temperatures are forecast to fall this weekend as cooler air moves down from the north. England's south coast will be warmest on Saturday with an expected high of 21C, while Sunday will peak nearer 17C.
The highest temperature recorded so far this year was 21.3C in Northolt, west London, and Chertsey, Surrey, on 20 March - but that figure is expected to be beaten on Friday.
Last month was the sunniest March in England since records began in 1910, according to the Met Office. It was also very dry, with the UK's rainfall total just 43% of the usual amount.
Average temperatures for this time of year are about 12C (53F) in England and 10C (50F) in Scotland, but parts of southern England hit highs of 20.7C on Thursday and 20.1C in the Scottish Highlands.
Speaking on Thursday, Met Office forecaster Dan Stroud said much of the UK "is looking at another fine and dry spring day", adding that while there will be "a lot of warm sunshine on offer", there will be some "cool temperatures near the east coast".
It is expected to be slightly cooler at the weekend, with winds expected to remain strong.
The public is being urged to avoid lighting fires outdoors over concerns they could spread bringing a risk of wildfires due to the warm, dry conditions.
Scottish Fire and Rescue Service (SFRS) said on Wednesday that there was a "very high to extreme risk" of fires spreading.
The fire service has tackled blazes this week near Bonhill in West Dunbartonshire and in the Kilpatrick Hills near Milngavie, East Dunbartonshire.
Elsewhere, more than 126 acres (51 hectares) were left charred after a fire at Upton Heath in Poole shortly before midnight on Wednesday, and a second fire broke out at nearby Canford Heath on Thursday morning.
Dorset & Wiltshire Fire and Rescue Service said the fires were both "down to human intervention".
In England there were 185.8 hours of sunshine in March, the Met Office says, the country recorded its sixth driest March and Wales its fourth driest since records began in 1836.