The price of diesel has almost reached parity with petrol in many parts of the country.

According to the AA, today's national average prices show the gap between petrol and diesel is now just over half-a-pence per litre.

This time last year, the gap was 13.85p per litre, meaning the difference between the cost of the two fuels has dropped 90% in a year.

This is the first time since 2001 that the prices have been so closely matched.

Diesel-engined cars get 15-20% more miles per gallon than most petrol equivalents.

However, a diesel car often costs around £1,000 more than a petrol one and breaking even can come after 40,000 miles.

Last July, when the average saving was 1.38p a mile, this break-even point came after 72,464 miles.

However, fleet managers have been warned that it is unlikely that price parity will be maintained, with the likelihood that diesel prices will rise more rapidly than petrol in the coming months.

“The current closing of the price gap results from a glut of diesel, caused by recession-hit industrial and transport demand, restraining price increases while petrol prices have soared in recent months,” explained Edmund King, the AA's president.

“Once the global economy begins to recover, demand for diesel will pick up and the price difference will open up again.”

Cars that average less than 15,000 miles a year are unlikely to recoup the initial extra cost of a new diesel car within their first three years, advised the AA.