Car chipping used to be a murky business. Boy racers would meet furtively with oily mechanics in a backstreet workshop dotted with carcasses of cannibalised cars. It had a certain under-the-counter glamour, like the porn shops of Soho in the 1950s before they became “table dancing” bars.

However, like these establishments, it seems “chipping” has moved into the mainstream and gained middle-class respectability – and it’s all due to the spiralling cost of fuel.

For those unacquainted with the black arts of chipping – or “engine remapping”, as its practitioners refer to it – the premise is simple: by tinkering with the software of the car’s onboard computer you can coax extra power and increased fuel economy out of it. The process takes a couple of hours and costs vary, but companies that perform the task claim fuel economy can be boosted by up to 16%.

This means that a standard diesel Audi A3 1.9 TDI can see its mileage per gallon increase from 62 miles to 72 miles. At today’s inflated prices – last week the average price of a gallon of diesel stood at £5.86p – that equates to a saving of about 94.5p per gallon. Fill up the tank (which holds just over 12 gallons) and drivers could be saving the equivalent of £11.34.

“Over the past few months we have seen a huge increase in the number of people that we wouldn’t normally expect to be contacting us, calling and asking about remapping their engines in order to increase fuel economy,” says Nigel Bennett, the managing director of Econotune, a chipping company. “In the past, people have been more interested in changing their engines to increase performance, but now it is all about fuel savings.”

All cars and many heavy goods vehicles such as those that brought part of London to a halt last week during the fuel protest can have their engines remapped. Results vary depending on driving style and fuel type, with diesel-powered engines fairing better than petrol. If cars can have their fuel economy and performance improved, however, why are the manufacturers not performing the operation at the factory gates? The answer is that like any product that is sold worldwide, car makers must produce performance figures that are consistent whether the car is driven in Abu Dhabi or Aylesbury. Because of this, and in order to get past the Single Vehicle Approval test (which forces cars to conform to British safety standards), car makers set the engine parameters to the lowest common denominator so it will perform equally well with low-grade fuel or bad servicing in, for example, eastern Europe, as it will in Britain.

“All we are doing is tweaking the engine so that it operates at its most efficient for the driving environment in Britain,” says Bennett.

As well as being more popular than ever, chipping has never been easier. The term dates back to the 1990s when tuning firms would replace the computer chip in the electronic control unit management system, thereby altering the dynamics of the engine. The process on modern cars can be achieved simply by plugging a laptop into a diagnostic port under the dashboard and reprogramming the engine remotely.

However, it is not all good news for eco-friendly (or just plain broke) motorists. Car makers warn that meddling with the engine can invalidate a warranty. This is still a grey area, though, and chipping companies claim the adjustments are often undetectable to a mechanic carrying out warranty work. Insurers are also sometimes reluctant to cover a car that has been tuned, and policyholders are required to inform them of any modifications to a vehicle.

Anyone hoping that increased fuel economy will result in lower CO2 emissions – and therefore a lower vehicle excise duty tax band – will be disappointed: cars are judged on manufacturers’ figures, and no amount of tinkering will persuade the Treasury otherwise. That is until someone decides to mount a challenge in court. And why not? If you can prove your car fits into a lower emissions group, why should you be penalised?

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