Anyone driving back home from their summer holidays in the last couple of weeks cannot have failed to notice that petrol and diesel prices are rising again.

The increase in UK pump prices during August was one of the biggest monthly jumps on record, according to the automotive services group RAC, which pointed to a rise of 7-8p on average in the cost of a litre of fuel to about ￡1.52-￡1.55 a litre. Higher petrol pump prices are not limited to the UK, with gasoline jumping in the US, Europe and Asia, too.

Part of this is easily explained by stronger crude oil prices in recent weeks — Brent crude has risen from $78 a barrel in mid-July to top $90 a barrel on Tuesday, largely driven by output cuts by Saudi Arabia and Russia. But a less well understood factor is refining costs.