The warnings precede a 10-day scorcher which is due to start this weekend and last until mid-July.
Temperatures are set to soar over the next few days as forecasters warn that extreme and sustained heat will push Britain into heatwave territory.
Softening of the highways could bring gravel about to sand the roads – a sight more common in the dead of winter.
RAC spokesman Rod Dennis said: ‘As the weather gets warmer so will the roads and you can pretty much guarantee the road temperature will be significantly warmer than the air temperature , especially where the sun is out.
“The heat can lead to some softening of road surfaces – more black patches of tarmac are the telltale sign.
“If the temperatures really rise, it may also be that sanding trucks need to be brought out as the salt can help improve the vehicle’s grip on the melting roads.”
Weather models reveal ground temperatures in the scorching sun reaching 40C by the middle of next week.
Air temperatures, more commonly used in weather forecasting, could top the 30C mark before the middle of the month.
James Madden, forecaster for Exacta Weather, said: “We are looking at an extended period of very hot weather from the weekend through the middle of the month.
“It could push temperatures into the 30Cs, with highs of 35C now possible in some isolated locations.
“This is a significant period of warm weather and could end up with the nation in the grip of a major heat wave.”
Soaring temperatures caused weather models to crash over the weekend, predicting air temperatures of 40C.
Unlike extremely high ground temperatures, 40C has never been recorded in a UK summer and is ‘highly unlikely’ next week.
John Hammond, meteorologist for Weathertrending, said: “One or two computer models point to temperatures as high as 40C in the next week or two.
“That would be unprecedented but highly unlikely.”
The mercury will start to soar from today, reaching mid to high 20C by the end of the week and even 30C over the weekend, he warned.
He said: “After the middle of the week with longer sunshine and light winds, temperatures will start to climb quite noticeably into the mid to high 20Cs in southern and eastern regions and at weekends. end, not far from 30°C.
“It will likely be the southernmost areas that will see the peak of the heat and it will be particularly around the coastal areas where there will be less cloudiness.”
“The south and east will see the highest temperatures later this week.”
“Next week the heat will continue with high pressure prevailing and I don’t see much sign of significant rain for several days to come.”
Scotland and northern England are expected to remain cooler in a northwesterly wind and could see rain, he added.
Drought fears amid forecasts of no rain in parts of the UK have raised fears of watering bans and water shortages.
Authorities have urged Britons to use water wisely while taking showers instead of baths and using washing machines sparingly.
Jim Dale, meteorologist for the UK Meteorological Service, said: “I see a period of 10 days to two weeks where in some parts of the country there will be no rain at all.”
“It could be problematic with the drop in river levels and would push these areas into a drought situation.”
The heat wave will be caused by a huge region of high pressure in the Atlantic and about to engulf Britain, he explained.
He said: “The Azores High will start to expand across Britain over the next few days and it’s over the weekend that temperatures could really start to rise.
“That’s the picture until about the middle of the month, and although we widely expect to see temperatures in the 20Cs, it wouldn’t be out of the question to reach 30C.”
The bookmakers slashed the odds on a series of hot weather odds with Coral offering 1-2 on a garden hose ban and 4-5 from 2-1 on the record 38.7C melt.
Spokesman John Hill said: “With temperatures steadily rising, we have reduced the chance that the UK’s highest temperature on record will be exceeded this month.
“We look set to have a spell of dry weather over the next few weeks, and following that forecast, we are now pushing for the UK to impose a garden hose ban this summer.”
Ladbrokes offers 10-11 on temperatures over the next week, bringing home the hottest July on record.
Spokesman Alex Apati said: “There’s every chance this month will be the hottest July ever, if the odds are good.”