Buses in Oxford have been fitted with pioneering 'spy in the cab' technology which helps drivers to save 10 per cent on fuel consumption.

Oxford Bus Company’s £125,000 'telematics' system, which keeps track of acceleration and braking, and encourages drivers not to leave engines idling, has been a big success during its 18-month trial.

Now it is to be rolled out nationwide by the company's owners, Go-Ahead group.

Go-Ahead is investing £3m in the technology and said it should start to repays its investment within a year-and-a-half.

The device, which sits on the right of the steering wheel, has five displays which light up to indicate revving, idling, braking, acceleration or excess speed. The speed limit is checked by global positioning system (GPS).

Operations director Louisa Weeks said: "We trialled the system on the busy City2 route and the results were dramatic.

"It was even more successful than we hoped for. We planned on achieving a reduction of around five per cent but the 10 per cent figure is a tremendous tribute to the hard work everyone has put in.

"With the new equipment and the training, our drivers now know just how much or how little fuel they are using.

"The monitor helps them with that target. It also reminds our drivers of the 20mph speed limit in the city centre.

"It’s had quite an effect on our drivers. Quite a few of them have been using the techniques they’ve learned at work when they are driving their own cars and they’ve had just as dramatic results. We believe the whole of Oxford will benefit greatly from the new technology.

"Everyone is better off because of even lower emissions and the results of the trials were so encouraging that we were able to factor the savings into our fare calculations this summer. As a result the increase was lower than it would have been without the system."

All drivers are expected to be trained and all Oxford Bus Company's buses fitted with the equipment by the end of the month.

Since being taken over by Go-Ahead in 1994, the company has seen a 50 per cent increase in customers, and now almost half of those travelling to the city centre arrive by bus.