Motorists could be slapped with an £80 fine for making a simple error while behind the wheel with hot weather set to hit the UK this weekend. In searing heat, many motorists will leave their engine running when parked up to make sure they keep their air conditioning turned on.

The air con will not work with the engine turned off meaning the only way to keep a steady stream of cool air entering the cabin is to leave the motor ticking over. This may appear harmless but road users may not be aware this could massively backfire due to a simple rule. The Highway Code states road users “must not leave a vehicle’s engine running unnecessarily while that vehicle is stationary on a public road”.

Graham Conway, spokesperson for Select Car Leasing warned road users could be fined even if they were unaware of the policy. 

He said: “With most typical cars, the air conditioning system ceases to operate properly when the engine is turned off. 

“You can go from feeling crisp and cool to clammy and uncomfortable in a matter of minutes, particularly during the spring and summer months.

“But while it might be tempting to leave the engine idling while you're parked, particularly if a friend or family member has just nipped to the shops or if you have a young child asleep in the back, it’s a bad habit we all need to be mindful of.

“Most motorists take a dim view of those who unnecessarily idle their engines and you risk a stern word from passersby. 

“What’s more, it’s also an offence under the Road Vehicles (Construction and Use) Regulations 1986 act which could see you hit with a fine.”

According to WeBuyAnyCar, motorists could face a fine upwards of £20 for breaking the simple rule. 

However, as per the Road Traffic (Vehicle Emissions) Regulations of 2002, the penalty is as much as £80 for those caught idling in Central London.

Idling engines are banned as they negatively contribute to air pollution in the atmosphere. 

These vehicles can churn out almost twice as many emissions with harmful particulate matter and nitrogen dioxide pumped onto streets. 

But, the RAC has warned many road users could escape the fines if they simply turn off their engine when asked. 

They said: “It’s important to note that fines are imposed only if a motorist refuses to switch off their engine when asked to do so by an authorised person.”