Are we paying more for diesel than we should be? The AA certainly thinks so as its research has discovered the gap between petrol and diesel should be much closer than it currently is.

Diesel is currently 4.4p per litre more than petrol on forecourts despite wholesale prices being very similar. In short, it looks like diesel buyers are being ripped off.

Between March 21 and April 18 this year, wholesale diesel prices ranged from the same price as petrol to up to 2p per litre cheaper. Yet during April, diesel remained at 5.4p per litre more expensive at the pumps.

Since then, diesel has again become closer to and even cheaper than petrol at wholesale but remains at least 4p per litre more expensive for motorists at the pumps.

The AA says prices on the UK's forecourts are not reflecting the fluctuating costs of crude oil and motorists are not receiving the savings they should be.

AA president Edmund King said: "The AA welcomes the OFT investigation but not at the expense of immediate and easily-achieved price transparency.

"If the EU can publish a weekly track of petrol and diesel wholesale prices in euros per tonne, why can't the UK government publish an equivalent?"