Petrol and diesel prices jumped again in March on the back of surging oil prices, bringing further misery to hard-pressed drivers.

Unleaded is now up almost 6p since the start of the year

Unleaded rose by nearly 2p a litre  (1.86p), from 144.62p to 146.48p, and is now up almost 6p since the start of the year.

Diesel went up by more than a penny (1.31p), from 154.68p to 155.99p, making for three consecutive months of rises, according to the data from the RAC and Competition and Markets Authority (CMA).

The increase in forecourt prices was driven by a 5% rise in the cost of a barrel of oil in March, alongside a pre-summer surge in demand for petrol in the United States, which caused the wholesale price of unleaded to rise to match that of diesel.

This rise has “squeezed” the average retailer margin on unleaded, from 10.5p at the start of March to 8p a litre, although the average margin on diesel rose by a penny to 11p over the same period.

Among the big four supermarkets, Asda has lost its crown as the cheapest fuel retailer, now assumed by Tesco, which had the cheapest average unleaded on 31 March at an average of 142.7p across its 511 forecourts. The RAC also noted a whopping 34p price difference between Asda’s cheapest and most expensive petrol (138.7p v 172.9p), while Tesco had the smallest difference between its prices at just 6p (138.9p v 144.9p).

Sainsbury’s and Tesco tied for the lowest average diesel price across their portfolios at 151.7p and 151.8p. Asda’s gap between its cheapest and most expensive diesel was 35.2p (147.7p v 182.9p), while Tesco again had the smallest gap of just 6p between diesel at its forecourts (148.9p v 154.9p).

The data also reveals that Asda, Sainsbury’s and Morrisons only offer their cheapest prices at one or two stores whereas Tesco offers it at around 30 forecourts, albeit at a slightly higher cost.

BP and Shell-operated forecourts also had significant differences between their cheapest and highest fuel prices. For unleaded, BP had a gap of 27p (142.9p v 169.9p) and Shell 26p (143.9p v 169.9p) across their 287 and 536 forecourts. For diesel, it was 30p for BP (149.9p v 179.9p) and 26p for Shell (153.9p v 179.9p).

RAC fuel spokesman Simon Williams said: “Sadly, Asda appears not to be the force it once was in fuel retailing. Gone are the days when it used to announce big headline-grabbing pump price cuts when wholesale prices fell, along with a promise at the time that drivers would never pay more than a certain low price at any of its forecourts.

“The data from the competition watchdog also highlights the wildly different prices BP and Shell charge at the forecourts they own and run. Worryingly, there is sometimes as much as 30p between their high and low prices. We badly need to see an end to this practice as this postcode lottery is extremely unfair on drivers.”

The RAC however welcomed the fall in the average retailer margin on petrol – most likely due to the increase in the wholesale price of petrol, but also possibly the result of the CMA again raising concerns about higher retailer margins very publicly last week.

In its latest report, the competition watchdog highlighted that fuel retailer profit margins remain at the high levels seen during its market study published in July 2023.

In 2017, supermarkets recorded margins of 4%, rising to 7.6% in 2022 (the year the CMA carried out its market study) and 7.8% in 2023. For other retailers, margins were 6.4% in 2017, increasing to 7.3% in 2022 and 9.1% in 2023.

The CMA said the sustained increase was concerning and supported the market study’s key finding that overall levels of “competitive intensity” have weakened in the road fuel retail market – underscoring its recommendations for new Pumpwatch powers so drivers can access real-time price data to boost competition.