Motorists wishing to fill up their cars at Tesco, Asda, Morrisons and Sainsbury’s are being advised to remove any roof racks from their cars beforehand. This advice is intended to reduce fuel consumption.

Sam Sheehan, motoring editor at Cinch, reinforced this advice, saying, “Roof racks and roof boxes can create drag, causing your vehicle to consume more fuel due to what is known as the drag effect.”

He continued: “Studies have shown that an empty roof rack can increase drag by around 16 per cent at 120 km/h, while an unused roof box can increase drag by up to 39 per cent.” Leaving these fixings in place can result in significantly higher fuel consumption, reports Birmingham Live.

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Therefore, he advises: “If you are not using your roof rack or roof box, remove it to save money and minimise your emissions.” Further research from industry experts at What Car? True MPG confirms that vehicles with roof racks can have 27 per cent lower fuel consumption.

Despite the obvious space saving of a roof box, it may not be a budget-friendly option, with prices starting at £130 and going up to £750. Additional kits, foot packs and roof bars could cost a further £200, and that doesn’t include the potential cost of professional fitting.

Jim Holder, editor of What Car?, said: “The vast majority of cars cannot achieve the official MPG figures given by manufacturers even without the fitting of a roof box. Fitting the box increases the overall weight of the car and increases aerodynamic drag, so it stands to reason that this will have a negative impact on fuel economy.”

“Taking a holiday to the UK may seem like a sensible way to save some money, but you’re actually paying for it in other, less obvious ways.”