"It's extraordinary," commented Ian Hobday, CEO of Liberty Electric Cars, who is striving to make battery-powered cars as efficient and cost-effective as possible.

"In a smaller car, if you put two very fat people in it, you will increase fuel consumption, that's for sure. And that's no different in an electric vehicle, except that the cost of your fuel is 20 per cent of the cost of petrol or diesel."

Thinner steel, plant-based plastics, lighter car parts, foam-filled seats, carbon fibre technology, the list is exhaustive. Car makers go to great lengths and spend £millions to make their vehicles lighter but their efforts are being hampered by the increasing waistlines of Britons.

With 40 per cent of Glaswegians being obese or morbidly obese, according to Nuffield Health - the UK's largest health charity - an NHS doctor from the City of Glasgow, who wished to remain anonymous, concluded the mileage achieved by many drivers in Glasgow is likely to be far less than the mileage of drivers in most other British cities.

Mr Hobday explained how many car manufacturers advertise a mileage which can rarely be achieved in the real world. "When mileage is calculated, it's based on a number of standards. It's based on a standard route that a car follows with traffic lights and hills so everyone's on a level playing field.

"It's based on an assumption of a certain amount of weight for the people in the vehicle and a number of assumptions that are probably false, like, for example, the heating or air conditioning are not turned on and the radio doesn't work. So they do everything within reason to get that mileage as high as they possibly can."

Doctors frequently attribute preventable car crash injuries to a lack of exercise - the most common being whiplash, with healthy people recovering far quicker than their overweight counterparts.