The average price of petrol rose by half a penny to 189.84p on Wednesday, while diesel was up by nearly 1p to 198p a litre.

This takes the cost of filling up an average 55-litre family car with unleaded to £104.41 while the equivalent cost for diesel drivers stands at £108.90.

RAC fuel spokesman Simon Williams said: “It seems as though we are just days away from the frightening prospect of the price of diesel averaging £2 a litre across the UK taking the cost of a full tank to a staggering £110. For drivers who still think in gallons this would be £9 a gallon.”

Williams added that they are “surprised and disappointed” to see the price of unleaded continuing to rise as the cost on the wholesale market “tells a very different story”.

He explained that over the course of last week delivered wholesale petrol averaged 148p a litre which should lead to a price of around 186p after factoring in 7p-a-litre retailer margin and VAT at 20%.

“We suspect if retailers fail to reduce their prices in the next few days they will find themselves playing into the hands of the Competition and Markets Authority which is currently looking into their behaviour,” he said.

Meanwhile, the average price of a litre at motorway services is now 203.45p for petrol and 205.88p diesel. Supermarkets – which tend to be cheaper – are recording an average price of 187.83p for petrol and 196.21p diesel.

The price of supermarket diesel has rocketed by 11p a litre in the last fortnight.