Motorists could be just weeks away from diesel prices falling below £1 a litre.

Diesel has fallen to a five-year low in recent weeks with a litre available for as little as 105.7p earlier this week due to faltering global economic growth.

Motorists are paying less to fill their cars with diesel than petrol for the first time in 14 years as forecourts pass on a big drop in wholesale prices.

Now experts are predicting they could be paying less than £1 a litre soon with no signs of the global economic position changing.

RAC spokesman Rod Dennis said: "This summer has been a much cheaper one for motorists than the last. The cost of filling up an average family petrol car is now around £8 less than it was last summer, and around £12 less for a diesel car.

"If the conditions stay right, we could see some even lower prices in a few weeks as people return to work after the summer and the school run begins again.

"And if Brent Crude were to move to the 40 dollar per barrel mark, the prospect of some enterprising retailers selling fuel for £1 per litre will make a return."

Jamie Winter, services director for Morrisons, added: "The current weakness in world markets is working in the favour of motorists because plummeting oil prices are combining with a strong pound to help us reduce petrol prices."

The decline in diesel bills has come as international crude oil prices have fallen by a quarter since early July. The wholesale price, which includes UK taxes, has fallen to about 85p a litre while petrol is closer to 88p.

As a result, the average cost of a litre of diesel in the UK has fallen below £1.12, compared with £1.15 for petrol, according to the Petrol Retailers' Association.

The AA has been campaigning this summer for garages to lower diesel prices since the wholesale price first moved to parity with petrol in May.

The cheapest diesel in the region on Wednesday was at Asda in Oldbury at 105.7p per litre.

It was also below 106p at Asda in Minworth and Great Bridge, Morrisons in Tamworth, Castle Bromwich and Redditch, and Sainsbury's in Castle Vale and Oldbury.

James Hookham, deputy chief executive of the Freight Transport Association, agreed the recent drop in prices might not last.

"We must highlight there is nothing sinister going on and prices could go up as quickly as they are falling," he said. "It is a very volatile market."