Drivers are being urged to follow this 'little-known' petrol pump trick that could save them up to £500 on fuel.

Motorists across the country often level off their petrol purchase to nice round pound (it's quite satisfying, isn't it?)

However, motoring experts have now advised drivers to stop making this costly habit.

The simplest way to claw back some cash when you fill up your tank is to avoid aiming for an even number, according to Select Car Leasing.

Instead, drivers are being encouraged to stop as soon as the pump clicks to a halt for the first time.

“Squeezing the fuel pump after the first click, also known as ‘topping off’, might seem like the right thing to do so you can make it up to the nearest pound, but it’s really not," Graham Conway, managing director of Select Car Leasing, said.

Graham continued: “That’s because it’s likely to still dispense some fuel that won’t end up in your tank".

The expert warned that if you ignore the first click you could be filling past the top of the fuel tank port, and that extra fuel will end up running into the small drain under the entry and onto the ground beneath your vehicle.

He noted: “On some pumps the extra fuel may be sucked back into the pipe. This means you are paying the petrol station to give them back their own fuel.

“A more serious issue, one that could damage your car and cost you serious cash, is connected to the vapour recovery system.

“This prevents evaporated petrol or diesel escaping when you release the petrol cap to fill up, capturing it in a charcoal canister instead.

“But if you are forcing surplus petrol or diesel into the tank, this can propel liquid fuel into the pipes and damage the vapour recovery system.

“That means you will soon see warning lights on your dashboard and run the risk of failing emissions tests".

Graham also warned that you'll also be looking at an expensive repair bill which could cost you up to £500.

Why do we fill up to the nearest pound? It's a habit that dates back to when all transactions were done with cash.

It made life simpler - if you rounded up to £20 worth of fuel then you wouldn't be left digging for coins in the glovebox and could instead hand over a crisp banknote.

Of course, now the vast majority of people pay with their credit or debit cards.

In fact, many motorists now use the common ‘pay at pump’ facility so there’s much less need to hit a specific mark.

Select Car Leasing’s Mr Conway said: “Many people have a slightly obsessive compulsive side to their character, so it is understandable that they want to reach a nice round number.

“But with the majority now shunning cash for cards, and apps such as Apple Pay and Google Pay, there is less need to be so accurate.

“It also removes the frustration of carefully trying to get to a certain mark and the counter somehow ticking over by a penny – an experience most will have had at some point.”