It was reported that by early afternoon, the temperature in Aboyne in Aberdeenshire had hit 30.2C, beating its previous high of 30.1C in 2018.
Across the UK, train services have been cut, schools closed and ambulance crews are braced for a rise in 999 calls as temperatures soar.
Temperatures had risen to 37.5C in Cavendish, Suffolk, and 37.4C in Kew Gardens, west London, by 3pm, making it the hottest day of the year, and the mercury topped 37C in a number of other places.
The Met Office was forecasting temperatures could climb to 38C or even a record-breaking 39C on Monday.
Wales has provisionally recorded its hottest day on record, with the temperature reaching 35.3C in Gogerddan, near Aberystwyth, beating the previous record for the country which has been in place since 1990.
Tuesday is predicted to be even hotter, with temperatures possibly reaching a “crazy” 41C in Yorkshire and Lincolnshire.
The existing UK record, of 38.7C, recorded in Cambridge in 2019, looks certain to fall amid the sweltering heat.
Met Office meteorologist Luke Miall said: “For a good part of eastern Wales, and England and southern Scotland, we’re looking at the 30s if not the high 30s.” He added that London could see temperatures hit 40C.
He said: “I’ve been a qualified meteorologist for 10 years, and telling people about 41C in the UK doesn’t seem real.
“It’s crazy how we are talking about these sorts of values, I’ve never seen the models coming up with these values.
“It’s been quite an eye-opener to climate change with all these temperatures in the UK.”
Meanwhile, speed restrictions have been put in place on key rail routes in Scotland.
Rail services hit
Network Rail confirmed train speeds would be restricted between 1pm and 8pm on Monday, which will have an impact on most routes, with a 20mph speed restriction on the stretch of rail between Hyndland and Finnieston in Glasgow, which is thought to be the busiest route in Scotland.
Network Rail tweeted: “We will be implementing further speed restrictions between 13:00-20:00 today. These restrictions will impact most train routes during the warmest part of the day, helping to minimise potential damage caused by todays forecasted temperatures.”
Restrictions will be in place between Glasgow Central and Edinburgh Waverley; Dumfries and Carlisle as well as Glasgow Queen Street and Aberdeen; Inverness; Oban and Fort William and Edinburgh Waverley and North Berwick, with delays of around 10 minutes expected, according to the ScotRail website.
The train operator urged passengers to “plan ahead”, tweeting: “Please please please, plan ahead if you’re out, it’s going to be extremely hot later today. Take water with you, wear sensible clothing – hats/sunglasses, if you’ve got elderly neighbours/relatives, check up on them.”
In Glasgow, ScotRail warned rail passengers they may face delays as overhead lines were tripping and resetting due to the heat between Glasgow Queen Street Low Level and Hyndland.
While hot weather is expected for much of Monday and Tuesday, meteorologist Jim Dale told BBC Radio Scotland’s Good Morning Scotland programme that no repeats are expected over the next few weeks.
He said: “This event is quite unusual. Last time the records were broken it was in a single day and it was just a spike here and there.
“Because we live, particularly in Scotland, in a temperate zone, what we’re not talking about is continuous, extreme heat that’s going to go on and on and on.
“These are always going to be spikes. I can’t see anything at the moment on the charts that suggest, certainly for Scotland, and even down into the London area, that suggest any repeats of this in the next couple of weeks.”
Meanwhile, Nicola Sturgeon told people to “follow sensible advice” as temperatures soar.
The First Minister tweeted: “The next couple of days are set to be exceptionally hot. Please take care and follow sensible advice – keep out of direct sun; stay well hydrated; and look out for others who may be suffering from the heat.”