Supermarket fuel prices were roughly 5p more expensive per litre in 2022 than pre-pandemic levels, an investigation by the competition watchdog has found.

The Competition and Markets Authority (CMA) has said that factors beyond the invasion of Ukraine have impacted the price customers are paying at the pumps and weak competition has helped drive increases.

Retailers, specifically supermarkets, came in for criticism from the regulator.

“Higher pump prices cannot be attributed solely to factors outside the control of the retailers”, the CMA said.

Evidence provided by the supermarkets, as part of the CMA’s road fuel market study, also received criticism.

“Whilst the level of engagement with the study has varied across supermarkets, we are not satisfied that they have all been sufficiently forthcoming with the evidence they have provided,” the CMA said.

“In particular, important information has only been received late in the day and after several rounds of information gathering.

“Given the concerns we have about a market of such importance to millions of drivers it is vital we get to the bottom of what is going on.”

In an effort to “get to the heart of the issues”, the CMA will conduct “formal interviews” with the senior management of supermarkets.

The CMA did add that supermarkets still tend to be the cheapest retail suppliers of fuel but found evidence indicating “at least one” supermarket has “significantly increased” its internal forward-looking fuel margin targets.

Other supermarkets have recognised this and may have changed their pricing behaviour accordingly, the regulator said.

Concern was also expressed over possible evidence of weaker competition in diesel compared to petrol since the start of this year.

High diesel margins seen this year “appear to have gone on longer than would be expected”, the body said, though some degree of variation is to be expected given the volatile diesel wholesale prices.

The watchdog has also been investigating price rises in the grocery market and announced it is stepping up its work to see if there are any competition failures which may contribute to grocery prices being higher.

So far the body said global factors have been the main driver of grocery price increases and it has not seen evidence of specific competition concerns in the grocery sector.