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Drivers don't realise that pressing a simple button can drastically cut down the fuel they are using on hot days. Appearing on BBC Morning Live one expert said that pressing it can mean the air conditioning system isn't overwhelmed with hot air flooding in.

Consumer expert Harry Kind was speaking after presenter Rav Wilding asked about having car windows open and the impact it has on economy. Rav said his car 'shouts at me' when he's driving with the windows open - and asked if it was lying about wasting fuel.

Mr Kind said: "It's kind of telling the truth - if you were driving very fast then keeping your windows down will increase drag. That is bad for your car. If you're going slowly your air con is probably going to use a lot more fuel so it would be worth opening the windows on a hot day through a city to get rid of the hot air inside and if you are going to use air con use the recirculation mode. That will keep the cost down, but ultimately going down the motorway with your windows down - not so great."

Using recirculation mode even with the air con off can help in terms of keeping the temperature down too. As the UK basks in a period of hot temperatures drivers have been advised to use the dashboard button that can cool down your car.

This button, marked with a small arrow and a symbol representing the interior of a car, is the 'recirculate air' button - an excellent method to cool down your car even when the aircon is off. As the name suggests, it blocks all outside air and only recirculates the existing air within the car.

It also benefits hayfever sufferers as it prevents fresh pollen from entering through your vents. It means that car isn't continually heated up by more hot air coming in from outside.

One method is putting the air conditioning, which uses a lot of power and therefore fuel, or battery, for a bit and then just using the recirculation button. Also if the air con is drawing hot air from outside then it has to cool that down using more power. If it's coolingthe already cooler air inside the vehicle, it's more efficient.

The RAC advises: "Once the air conditioning is blowing cold, close all the windows and switch to (pre-cooled) recirculated air. You can now open the upper air vents and adjust the flow as required. More advanced 'climate control' air-conditioning systems allow you to set and maintain a constant temperature within the car."

On BBC Morning Live this week Mr Kind also advised people to cut their speeds on the motorway to reduce fuel costs - and said a small amount can make a big difference. He said: "What makes a huge difference way more than the price of fuel is how you drive. "When you are motoring along I would say reduce your speed. This is one of the biggest factors. The Department for Transport says that going down from 80 to 70 miles per hour saves you 25 per cent on your fuel and also it's not illegal.

"Then when you go down from 70 to 60 that will save you about 9 per cent. The savings get less and less as you get slower and slower.

"When you're driving along at those speeds, make sure you're going consistently, you're not breaking all the time, and ideally use cruise control."