With drivers travelling in sweltering temperatures, there is one tiny button in the car that motoring experts say should be switched on during the heatwave.

With the hot weather, holiday travel and Saturday's rail strike expected to lead to difficult driving conditions for many, motorists may be paying closer attention than ever as to how best to keep vehicles cool.

For those with air conditioning in their cars, switching on the recirculation button - which is usually marked with a car icon and a sideways-shapped arrow inside it - will not only help keep passengers more comfortable but will also lower fuel consumption and encourage a car's unit to last for longer.

Graham Conway, managing director at Select Car Leasing, is among those reminding drivers about the little known switch that shouldn't be ignored during the ongoing hot spell.

Helping to recirculate existing air from inside the car, which has most likely already passed through and been cooled down significantly by the car's air conditioning system once already, means the vehicle doesn't have to work as hard to keep the inside temperatures lower.

Graham explained: "The recirculation button takes the air from inside your car and circulates it around instead of pulling in fresh air from outside, working with your AC to keep you cool and the perfect time to use this is in summer weather when the outside air is hot.

"By keeping hot air from outside out of the car and circulating the air already in there, your car will be much cooler when driving in the baking heat. The circulation of cooler air will make the drive much easier for both the driver and passengers, especially during a long journey with children or pets in the car."

Because the air conditioning doesn't have to work at an optimum level to continuously cool down the record-breaking hot air from around the outside of the car, using the button will also reduce strain on the system, keep air filters cleaner for longer which in turn will increase the longevity of car parts.

National Highways says it expects Saturday's day time traffic to be exceptionally busy with football fans heading for games and families enjoying the school break on changeover day at holiday lets, among those taking to the roads in greater numbers because of a lack of trains caused by the train drivers' strike.

With journeys expected to take longer and traffic jams anticipated, Graham suggests drivers can switch on the button as part of efforts to also use less fuel.

He added: "With the price of petrol and diesel higher than they’ve ever been before, everyone is looking for ways to save on fuel. In the hot weather, the air recirculation will assist the AC system which will reduce fuel consumption and also save power for the car’s battery to last longer."

And while leaving the windows down on hot days can increase the drag on the car - which then uses up more petrol or diesel - if the extreme temperatures outside have left the car baking in the sun then the advice is to bring the car windows down for a short while to release some of that hot air before switching on the air conditioning and the recirculation button.

Graham added: "If the car has been baking in the sun, then roll the windows down, turn the AC on and get rid of the hot air in the car before switching recirculate on, otherwise you’ll be stuck with hot air being recirculated."