Consumers could save more than £200 a year by seeking out the cheapest petrol stations, especially as prices have registered their biggest fall for 18 years over the past month.

The average price for a litre of unleaded petrol has tumbled to 88.07p from a peak of 98.54p on August 1, when markets were concerned about conflicts in oil-producing countries.

Since then, crude has fallen below $60, compared with a peak of $78 a barrel in August, although it has since rebounded to nearly $62.

Supermarkets are even cheaper than the average forecourt as they are engaged in a price war at the pumps. The cheapest supermarket fuel is from Asda, which recently cut the price of unleaded to 84.9p and diesel to 89.9p.

The most expensive is Morrisons, which charges 86.01p for unleaded and 91.55p for diesel.

The cheapest non-supermarket unleaded is from Shell at 87.46p, while Murco is the most expensive provider at 89.75p a litre.

However, there can be wide variations around the country. While Texaco has an average price of 89.36p, it is charging £1 at Harlech in Wales.

The most expensive price is £1.08 for unleaded at an independent filling station in Ely, Cambridgeshire.

BP has an average price of 88.79p a litre, but it was charging 92.9p at its station in Tulse Hill, south London last week.

Someone with a typical family car with a 50-litre engine would pay £42 a week to fill up their tank at Asda, compared with £46.45 at BP’s Tulse Hill garage — a saving of £231 over a year.

Luke Bosdet at the AA said: “The price falls are great news for motorists. It will make a huge difference to the family budget.”

Asda’s cut was the fifth in the past five weeks, while Tesco has also reduced its charges several times in recent months.

However, the Wal-Mart-owned Asda chain has a nationwide pricing policy whereas Tesco prices locally, making it difficult to compare costs.

Figures released by the fuel comparison firm Catalist show Tesco charging an average of 85.99p for unleaded and 90.97p for diesel.

Sainsbury’s cut its unleaded price by 1p to a flat rate of 85.91p last week, its ninth price cut in five weeks.

It is worth looking up local prices at petrolprices.com.

Kay Joyce at Petrolprices said: “While some firms such as Shell seem to be matching the competition from Tesco and Asda, BP is not doing so to the same extent, so it is always worth checking.”

For more on consumer affairs visit www.timesonline.co.uk/consumeraffairs