Friday's reading of 30C (86F) at Achnagart in Scotland surpassed the previous record of 28.9C for this year, set on 2 June.
But the sunshine will not last for everyone. For Saturday evening the Met Office has issued a severe weather warning for thunderstorms in Edinburgh, East Lothian and the Scottish Borders between the hours of 18:00 and 23:59.
A yellow warning for lightning is in place for Glasgow and Strathclyde, Fife, Moray, Aberdeenshire, Tayside and eastern parts of the Highlands.
The Scottish Environment Protection Agency (SEPA) has also issued a flood alert for Edinburgh and the Lothians, the second such warning in less than seven days after the Capital was drenched in a deluge on Monday 24 June.
Despite this, pollen counts and UV levels will be high or very high everywhere except in northern Scotland.
Met Office Meteorologist Luke Miall said: "It's going to be a very hot one for some parts of the UK today (Saturday).
"Yesterday (Friday), western areas saw the highest temperatures but today it's beginning to turn a bit fresher with heat transferring more towards the east.
He added: "Across parts of north-east England and south-east Scotland as a cold front pushes in we could see some thunderstorms later in the day"
In England, The Met Office said a reading of 30.8C (87.4F) was taken in Charlwood, Surrey, on Saturday morning, with temperatures expected to rise as high as 34C (93.2F) later in the day.
This would fall just short of the 35.6C (96F) June record set in 1976.
Glastonbury festival-goers will be treated to sunny and dry 31C (87.8F) conditions on Saturday afternoon.
Across the UK sales of barbecue food have soared, according to Tesco, with the supermarket predicting it will sell more than one million packs of sausages, 650,000 packs of burgers and 50,000 disposable barbecues over the weekend.
The predicted figure for sales of barbecue meat is double that of last weekend.
For Saturday the Met Office has issued a severe weather warning for lightning across areas in Northern Ireland and western Scotland, while a severe weather warning for thunderstorms spans the north-east of England and the south-east of Scotland.