RAC Fuel Watch found that petrol was 1p a litre cheaper in March than February and diesel 4p a litre cheaper.

By the end of the month, a litre of unleaded petrol was 146.5p (down from 147.56p), while diesel reduced to 162.94p (down from 167.06p) – its cheapest price since early March last year.

This means the price of petrol has fallen nearly 20p from 166p at the start of November, saving drivers almost £11 every time they fill up a 55-litre family car (£91.3 in November 2022 to £80.57 now).

Diesel, meanwhile, has dropped 27.5p from 190.5p, saving drivers a £15 a tank (£104.77 to £89.62).

But while the diesel pump price reduction appears dramatic, the RAC believes it should have been far greater as its wholesale price was very similar to petrol’s for most of March.

In fact, diesel became cheaper than petrol on the wholesale market on 23 March and has stayed that way since, finishing the month at 111.69p a litre compared to petrol at 115.81p.

The RAC calculates that the average retailer margin on a litre of diesel at the end of March was 21p – three times the long-term average of 7p. In contrast, the margin on petrol was just 7p.

Diesel drivers ‘ripped off at the pumps’

The RAC says the extent to which drivers of diesel vehicles are being taken advantage of is “blatantly apparent” when comparing the average price charged by retailers in Northern Ireland where it’s 10p cheaper at just 152.78p. Petrol is also 2.5p cheaper there – being sold for 143.97p at the end of March.

A number of factors make fuel cheaper in Northern Ireland, including a higher retailer-to-car ratio, more fuel distributors and sometimes cheaper fuel across the border. However, it should also be noted that the big four supermarkets don’t have the same hold on fuel retailing in Northern Ireland as they do in England, Wales and Scotland, with only 28% market share in stark contrast to 43% across the whole of the UK.

The average price of unleaded at one of the big four supermarkets fell by 1.5p in March to 143.18p and diesel by 5.3p to 159.88p. Asda had the cheapest petrol at 142.69p (down 1p) and Tesco had the lowest priced diesel at 159.58p (down 6p).

However, member-only retailer Costco is still offering the most competitively priced fuel across the UK with petrol at 137.7p and diesel at 149.8p.

‘Good news for drivers but diesel needs bigger cuts’

Simon Williams, RAC fuel spokesman, said: “The fifth consecutive fall in the price of fuel in as many months is without doubt good news for drivers, but those who run diesel vehicles should have enjoyed far bigger cuts at the pumps than they have actually seen.

“Knowing the average price in Northern Ireland is 10p cheaper at 152.78p is utterly galling for those on this side of the Irish Sea who rely on diesel, whether that’s for personal or business use.

“We hope the Competition and Markets Authority is paying close attention. The situation in Northern Ireland shows just how much diesel should really be being sold for. While there are several reasons why petrol and diesel are generally cheaper in Northern Ireland, it also can’t go unnoticed that the supermarkets aren’t as dominant in fuel retailing there as they are on the mainland.”