There is something wrong with the way many people are charged for their gas and electricity.

The big energy suppliers, which are the only ones left since the rising wholesale prices put the smaller operators out of business, have a multitude of tariffs.

It varies depending on your usage, depending on what type of meter you have, and if you are using a pre-payment meter the chances are you will be paying more per unit than most other people.

This is a big problem for many people, with around 450,000 homes in Scotland on prepayment meters.

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Often it is people on lower incomes who are on pre-payment meters.

Citizens Advice says pre-paying for your energy lets you pay small amounts often, but it’s usually a more expensive way to pay than getting a bill.

And if you run out of money you run out of gas and electricity.

It doesn’t stop there.

If you don’t use any energy the daily standing charges continue to rack up. So, if you self-disconnect for a few months and then put £20 on the prepayment card you will only get under a fiver’s worth of energy before it runs out.

The cost of an essential service like gas and electricity is supposedly regulated by Ofgem, but in fact, many people fear it is not really, or if it is, it is not geared towards the customer.

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Take the price cap. As soon as the energy companies said they need to put up prices the cap is raised higher and higher to make it pretty much meaningless.

The real problem though is the tariffs and pre-payment meter customers are charged more.

They are advertised as a way of helping people if they are struggling to budget, then charged more than someone else.

We all use the same gas and electricity so why are different people paying different amounts when they have the same provider?

For example, ten people go into the same supermarket and buy a two-litre carton of milk and a loaf of bread.

Those ten people are all charged the same amount for their bread and milk.

The supermarket doesn’t ask them how much milk they consume or how many loaves they ate in the last year and then offer them a price according to that information.

No, the price of a carton of milk is the price of a carton of milk. A loaf of bread is a loaf of bread.

So, why should the price of a unit of energy be different?

It is the same with petrol. The price per litre you pay is not dependent on how many miles you drive in a year or what size of car you have.

On their websites they all offer the service, ‘get a quote’.

There are several tariffs across the market including fixed rate, variable rate, which could change month to month, dual fuel, capped, unlimited, pre-payment, smart, green and economy.

Economy charged less for off-peak times but can charge more at other times.

Imagine going into a supermarket and the shop assistant asks 'when will you be eating your bread' before determining the price they want you to pay.

“Oh you’re planning on eating a piece at three in the afternoon, sir. That will cost more, it will be cheaper if you have a sandwich at three in the morning, sir.”

The companies say it is to give the customer the best tariff to suit their individual circumstances.

But why do they have so many different tariffs and most importantly why do people on pre-payment meters have to pay more per unit than others, especially when often they are the least likely to afford it?

The Glasgow Times contacted the big six energy providers and asked them the same question.

We contacted ScottishPower, British Gas, Ovo Energy, E-on, EDF and Npower and asked this: “Could you please supply a list of various tariffs offered for domestic customers and explain why there needs to be different tariffs.

“Can you also state whether people on pre-payment meters are usually on a higher tariff than many others and if so why would this be the case?”

Of the six contacted, none of them replied.

At the moment it is unlikely that switching from one supplier to another will make any difference.

On the British Gas website it states: “Due to continuous increases in wholesale energy prices we are unable to offer you any competitive fixed-rate tariffs at this moment in time. There's no need to call in as our agents also wont be able to provide any tariffs.”

When the cap goes up and bills rocket again pre-payment meters customers will be hit harder.

Martin Lewis, the money-saving expert, probably the person most worth listening to during this crisis, says on his website: “These rises are unaffordable for many on the lowest incomes.”

As usual, he is not wrong.