Is the already put-upon Shropshire motorist being taken for a ride?

It was sold as the ‘green’ fuel and years ago, in the dim and distant mists of time when it was still perceived as belting out thick black plumes of smoke, diesel used to be far cheaper than petrol.

That was one of the reasons people bought a diesel-powered car in the first place, along with the fact that their engines were supposed to be more fuel efficient and run for longer.

But in the last few years things have changed. Diesel was no longer cheaper. Last year the price overtook unleaded petrol by few pence per litre and the differential was ever widening – by 13p at some filling stations.

Today, as motorists trawling the service stations for the cheapest fuel, they find in some cases petrol is more expensive than diesel, and in other diesel is more expensive than petrol.

What is going on? Why, on some Shropshire forecourts, is unleaded more expensive?

Anyone with a GCSE in chemistry will tell you that diesel requires less refining than unleaded petrol, and uses less crude oil to produce. Why, then, did it become more expensive in recent times?

The answer – or at least part of the answer – is that our new, cleaner and greener diesel wasn’t actually as cheap to produce, at least not initially.

Although diesel requires less crude oil per litre than petrol does to produce, established standards for lower sulphur diesel required a more complex refining process.

And hey presto, the price of diesel at the pumps went up. The chap with the chemistry GCSE might have his clever equation, but so does the chap with the maths GCSE: greener equals more expensive.

But that was a few years ago now when diesel was taxed more heavily, so why, in some cases, is unleaded more expensive?

It could be that the majority of cars on the road in the UK – just about – still run on unleaded petrol and are thus more at the mercy of market forces, so there may be scope for increasingly competitive sale of unleaded petrol at the pumps.

Fluctuations between the prices of unleaded and diesel have in the past been a result of greater changes to unleaded prices than to diesel’s.

But, like the rest of us, Telford road campaigner Peter Roberts is at a loss to explain the difference in price today between fuels, although he says high-performance unleaded has always been more on a price par with diesel.

“It’s more down to what oil companies can get away with than anything,” he says. “The tax on both diesel and unleaded is the same. It is the whim of the oil companies who want to make a profit. There’s no logical reason.”

And so the jockeying between diesel and unleaded petrol prices continues. As the price nudges well over £1 a litre for both, at the moment it’s anyone’s race.

And motorists will have little choice but to go on coughing up for their fuel, whatever the cost.

By Ben Bentley