The average prices of supermarket petrol and diesel has increased every day since the end of March, setting a record for consecutive daily rises.
During that time more than 8ppl has been added to the average price at their pumps, analysis of RAC Fuel Watch data reveals.
Pump price data provided by Experian Catalist shows that on 26 March a litre of unleaded petrol bought at the big four supermarkets averaged 116.66p and diesel was 119.35p. Eight weeks later, on 23 May, their pump prices averaged 124.74ppl for petrol and 127.69ppl for diesel.
Overall average prices for the UK have increased even more over the same period as a result, rising almost 8.5ppl, although they have not increased every day. Petrol has gone up from 119.78ppl to 128.29ppl and diesel has increased from 122.54ppl to 131.15ppl.
The rises are due to the price of oil increasing to above $80, combined with a poor pound to dollar exchange rate of $1.33, which negatively affects the cost of fuel on the wholesale market as fuel is traded in dollars.
RAC fuel spokesman Simon Williams said: “This is the worst series of consecutive daily supermarket price rises we have seen since we began monitoring this three and a half years ago.
“The supermarkets are being very quick to pass on increases in the wholesale price of fuel brought about by a 17% rise in the price of oil to above $80. Sadly, RAC Fuel Watch data shows they are far faster at passing on rises in the wholesale price than they are falls.
“Supermarkets are highly influential in the price charged at pumps across the UK as, despite operating under 18% of all forecourts, they sell 45% of all fuel sold. While other fuel retailers don’t buy as frequently they will often match supermarket price rises which means they increase as the supermarkets do.
“Unfortunately, the higher oil price has come at a time when the pound has weakened considerably against the dollar. This causes pain at the pumps due to the fact that, similar to oil, fuel is traded in dollars so the lower the exchange rate, the worse the price gets for UK motorists.”
He added that forecasts suggested average petrol and diesel prices would rise by a further 1ppl over the next two weeks.