Diesel hit a six-year low in November and petrol fell below £1 per litre, as the price of barrel of oil tumbled to $40.40 – its lowest price since February 2009.

The average price of petrol reduced for the fifth month in a row, while diesel fell to its lowest average price since late December, 2009, when it reached 109.48p a litre on November, having started the month at 109.77p.

This means since this time last year the cost of filling up a 55-litre family car with petrol has plunged by £7.75 and a tank of diesel has come down even more, with a fill-up now £8.95 cheaper than a year ago.

The RAC Fuel Watch report shows a barrel of crude oil fell over $3 in November, coming down from $47.32 to $44.03, with the six-year low of $40.40 being seen on 16 November. Unfortunately, the pound lost a little ground to the dollar – with a pound worth $1.54 at the start of the month and $1.51 at the end – undoing some of the positive effect of the lower oil price as oil is traded in dollars.

RAC Fuel Watch spokesman Simon Williams said: “In the expensive run-up to Christmas, drivers of both petrol and diesel vehicles are benefitting from far cheaper fill-ups than they did at this time last year.

“While petrol for under a pound a litre has become a reality at the cheapest retailers we would like to see this happen on a non-promotional basis. This depends, of course, on the cost of a barrel of oil staying low and ideally trading down a little closer to $40 for longer – something which is very hard to predict, particularly as OPEC meet tomorrow in Vienna to discuss oil production strategy.

“There has been talk of stabilising the barrel price which would mean stemming production, but it’s difficult to see how that would work when Iran begins to pump up to one million barrels a day in 2016, following on from its landmark nuclear agreement with the West.

“The lower forecourt prices we’re enjoying at the moment are a product of the fall in world crude oil prices, which began in September 2014.

“After a six-year low of $45 a barrel in early February and two instances of going back up to the $60 level twice briefly since, the price has been consistently below $50 since mid-October, reaching a new six-year low in mid-November.

“As it stands we anticipate a very slight average petrol price reduction in the next two weeks and another 2p a litre coming off diesel, taking the new six-year average low price even lower.”

HMRC oil duty statistics for October show combined sales of petrol and diesel were 1.9% up on September at 3.905bn litres and up 1.8% on the previous October. Petrol sales (1.461bn litres) were static on September whereas October saw the fifth highest number of litres sold in any month since 1990 with 2.444bn. This was 2.9% up on the month before and 3.7% up on October 2014.