Scotland and Northern Ireland have each recorded their warmest day in years as the third heatwave of the summer peaks, with temperatures in Wales also potentially breaking records on Saturday.
The Met Office said that the Scottish town of Aviemore hit 30 degrees Celsius, adding that Scotland last exceeded the same temperature on June 13, 2023, while Magilligan saw the same high on Saturday, marking the first time the milestone had been reached in Northern Ireland since July 18, 2022.
Although England has been hot, with highs of 34 degrees Celsius forecast in parts of the country, temperatures are not expected to break the country's current record for 2025 of 35.8 degrees Celsius – recorded in the county of Kent at the beginning of July.
Amber heat health alerts are in place for central, southern and eastern parts of England until 9 am (0800 GMT) on Monday, warning of the potential for a rise in deaths, particularly among those aged 65 and over or with health conditions.
Tennis fans have been struggling in the heat at Wimbledon for the past few days, with play experiencing brief disruptions as spectators needed medical assistance.
With temperatures forecast to rise on Saturday, the All England Club said it has significantly increased the number of on screen communications and push notifications to remind guests to stay hydrated and seek respite from the sun.
The club also said service stewards on court have access to water for spectators in need, that on-site medical teams are ready to assist when required and that the grounds have more than 100 free water refill points as well as a pharmacy where guests can buy sunscreen.
On Friday, Wales recorded its hottest day of the year with 32.4 degrees Celsius in Cardiff's Bute Park and even the Scottish Highlands had very hot weather, with a high of 28.9 degrees Celsius in Aboyne, a village in Aberdeenshire.
In England, temperatures reached 34.7 degrees Celsius at Astwood Bank, near Worcester, on Friday.
Met Office meteorologist Greg Dewhurst told the PA news agency: "Yesterday was Wales' highest temperature of the year so far, so it'd be a similarish value, so we'll keep an eye on that today."
"And then Northern Ireland and Scotland, I think the highest of the year is just shy of 30C so for both of them, it could be slightly higher than those values."
"So quite, quite possible to see the highest temperatures of the year so far for parts of Northern Ireland and Scotland and Wales too, but England unlikely."
The average temperatures for this time of year across the United Kingdom range between 18 degrees Celsius and 22 degrees Celsius.
Dewhurst said the "vast majority" of the country is in for a sunny Saturday, with the exception of the eastern coast of the UK which may be a little cooler and cloudy at times.
"So anyone wanting a bit of relief from the heat, then all coastal stretches are cooler but particularly the east coast today," he told PA.
Fire chiefs have urged people to stay safe as they warned of the increased risk of wildfires and drowning.
The National Fire Chiefs Council (NFCC) asked people not to enter water to try to cool down and urged parents and carers to ensure children are supervised around water at all times.
Phil Garrigan, NFCC chairman, said: "We are urging people to take simple but vital safety precautions to protect themselves and their loved ones during this period of hot, dry weather."
"Our experience tells us that wildfires can start in an instant and escalate rapidly. That's why we're asking everyone to stay alert and act responsibly," he added.
The national coastguard also issued safety advice for people heading to the coast, as data from the water incident database shows most drownings happened in July over the last three years.
As well as the amber alerts, the UK Health Security Agency (UKHSA) has yellow alerts in place until Monday for the north-east, north-west and Yorkshire and Humber.
Yorkshire Water brought in restrictions on using hosepipes for activities such as watering the garden, cleaning cars and filling paddling pools, on Friday, as part of efforts to protect supplies in the face of yet more dry weather forecast for the coming weeks.
South East Water said demand for drinking water had reached "record levels since May," adding: "This situation has left us with no choice but to restrict the use of hosepipes and sprinklers, so we can help our reservoirs and underground water storage recover."
It means customers in the counties of Kent and Sussex are banned from using a hosepipe to water gardens and plants, clean vehicles, fill swimming pools or ponds or clean paths, walls or windows from July 18.
Those who ignore the bans could face fines of up to £1,000 ($1,350).
The London Fire Brigade said it has responded to 24 wildfires this year, five of which occurred this week, including one in east London on Friday, where 70 firefighters fought to tackle a grass fire.
The risk of wildfires in London is currently rated "severe" by the Natural Hazards Partnership.
Meanwhile, Scottish fire crews are spending a second day tackling a wildfire in Perth, as an "extreme" wildfire warning is in place for much of the nation.
The National Rail train network has warned train passengers that the hot weather may cause disruption this weekend.
"Heat can cause overhead lines to expand and sag, rails to buckle, and also line-side fires," it said on its website.
Meanwhile, the RNLI warned beachgoers that, despite the heat, there is still a risk of cold water shock.
Ross Macleod, the charity's water safety manager, said: "Even in hot weather, the seas around our coasts are cold enough year-round to trigger cold water shock, while waves and rip currents can overpower even the most experienced water users."
