Motorists whose vehicles lack efficient air conditioning are being advised to postpone non-essential travel during the current heatwave.
The RAC, which issued the urgent plea, also urged drivers to exercise “patience” as record demand is expected to lead to extended wait times for breakdown assistance.
This advice follows the Met Office’s red weather warning for extreme heat, in effect for Wednesday and Thursday.
RAC road safety spokesperson Rod Dennis said those warnings are “rare” and “we urge everyone to take them seriously this week”.
He went on: “Drivers whose vehicles don’t have effective air conditioning should strongly consider postponing any non-essential car journeys until the Met Office’s weather warnings are lifted and temperatures drop.
“If this isn’t possible, our best advice is to travel during cooler times of day.”
He said this week “could end up being a record-breaking one for June” in terms of the number of call-outs to broken down vehicles.
He added: “Our last busiest June was three years ago, but there’s every chance that could be eclipsed this week as temperatures soar.
“Today, we expect breakdown volumes to be around 20% higher than what’s normal for a Monday in late June.
“We ask anyone who breaks down to be patient while breakdown providers prioritise the most urgent roadside jobs.
“The heatwave will affect services right across the UK and while all patrols will be working incredibly hard to assist drivers, longer waits are more likely.”
AA president Edmund King said drivers “shouldn’t be surprised” to see gritters deployed.
The machines are normally used to distribute salt during the winter to stop ice forming on roads, but they can also be utilised to spread light dustings of sand in high temperatures.
Surface temperatures can reach towards 50C when air temperatures are in the “low-to-mid 30s”, Mr King said.
East Anglia saw a number of roads melting in heat last month, such as the A143 in Stanton, near Bury St Edmunds.
Mr King went on: “Some roads may begin to soften when surface temperatures get towards 50C, particularly older or more vulnerable surfaces.
“The main risk for drivers is not that the road suddenly ‘melts’ everywhere, but that patches can become tacky or uneven.
“That can affect braking, steering and grip, especially for motorcyclists and cyclists, and can also throw up loose material.”
Drivers who came across a softened road surface are advised to slow down, avoid hard braking or steering, and increase their distance from the vehicle in front.
Mr King said heat also puts extra strain on vehicles.
Tyres are more likely to fail in hot weather, particularly those that are under-inflated, damaged or old.
Mr King added that animals should not be left in parked cars even for a short time during high temperatures, as interiors “can soon get as hot as an oven”.
Meanwhile, train passengers are being warned over disruption because of the heat.
Great Western Railway said it is running fewer trains than normal between London Paddington and Reading until Friday.
This is because Network Rail is not moving some points – pieces of metal that enable trains to change tracks – on the route to cut the risk of failures, which are more likely in high temperatures.
There is disruption across the Transport for Wales network, including between Pontypridd and Cardiff Bay, and between Coryton and Penarth.
South Western Railway issued an alert stating that “services may be subject to short-notice cancellations and amendments”.
