Major retailers, including supermarkets, have accelerated their reduction of diesel prices following concerns raised by the Competition and Markets Authority (CMA) about weakening competition in the retail fuel market, according to analysis by the RAC.

Over a two-week period since 15th May, the average price of a litre of diesel at supermarkets dropped by 7.44p, from 151.02p to 143.58p.

The RAC has been urging large retailers to lower diesel prices since the end of March when the wholesale price fell below that of petrol.

However, while unleaded petrol was sold at around 143p per litre throughout April, the average diesel price at supermarket sites remained high, only seeing a reduction of 10p per litre (from 161.4p to 151.02p) in the month before the CMA announcement.

The gap between average petrol and diesel prices at supermarkets was 9p on May 15, but it has now narrowed to just 2.5p, indicating that retailers have been prompted into action by the CMA.

Nevertheless, the RAC believes that supermarket diesel prices should be around 6p per litre lower than their current level (137p) to reflect a fair price.