Motorists hoping for a staycation this weekend as schools shut for the summer holidays have been urged not to drive before 8pm.
Drivers have been told to avoid driving at peak times of the day as the mercury has climbed to a scorching 32C this week.
The Met Office recorded its hottest day of the year yesterday at Heathrow Airport of 32.2C - smashing the previous record that was set on Sunday.
Health experts from Public Health England issued a warning yesterday for people to stay safe during this week's heatwave.
Motoring groups are also issuing advice to drivers as more than 11million cars are expected to start taking trips over the next five days.
The RAC has asked motorists to be careful as more breakdowns can be expected.
Drivers who find themselves without water when they break down are at risk of becoming dehydrated among other health effects.
Motorists are facing a "perfect storm" as more are expected to take staycations instead of travelling abroad with the rapidly evolving traffic light system, the RAC said.
Trips within the UK has contributed to a 29 per cent increase in traffic on popular roads, it was added.
It comes as the Met Office has extended its extreme weather warning days after issuing its first-ever extreme heat-health warning this week.
The initial warning was in place until yesterday but has been extended to Friday, July 23.
PHE has also extended its heat-health alert until Friday as they urge those in the heatwave hotspots to exercise caution.
Dr Owen Landeg, Scientific and Technical Lead at PHE, said: "Everybody can be affected by high temperatures and most people are aware of good health advice for coping with hot weather.
"However, it’s important to keep checking on those who are most vulnerable such as older people and those with heart or lung conditions.
"As we experience the first hot weather episode of the year, it’s important for everyone to remember to adapt their behaviours. This is particularly important during the pandemic with many people self-isolating."
Chief Operational Meteorologist at the Met Office Steven Ramsdale said: "The high temperatures are going to continue through a large part of this week, with temperatures regularly in the high 20s and low 30s Celsius by day, along with high overnight temperatures.
"Many areas of the UK will continue to reach heatwave thresholds, and whilst the highest temperatures are likely to be in central and southern parts of the UK, some of the most unusually high temperatures are likely to be seen over parts of the West, particularly over Northern Ireland."
