By contrast, the engine in your petrol car is about 20-25% efficient.

On the road, the biggest difference you notice with the diesel is the need to change up a gear slightly earlier than in a petrol car.

By 1922 the cost of operating the one-carriage steam car proved to be more expensive than the new petrol cars.

I have a petrol car and a mortgage.

So the efficiency of electric cars is, in fact, comparable with petrol cars.

The hatchback model will be "much more expensive" than a comparable petrol car, a company spokesman admitted.

Based on a petrol car's design, this electric version does 0-62mph in 13secs and a top speed of 84mph.

The petrol car is more expensive to tax, however, costing £95 to the diesel's £20.

That is one of the reasons why diesels have better fuel efficiency than equivalent petrol cars.

I am now only driving about 10,000 miles per year so am thinking of a petrol car rather than another diesel.