Maria Johnson from Hillworth Stores in Devizes, Wiltshire, was mystified when her utility supplier, Eon, told her she had a zero credit score. Very odd as she had been with Eon for nine years and the previous year her credit rating had been 81%.

She writes: “This caused my electricity to cost me more as they couldn’t get a deal with British Gas. But my company has not 1p of debt, so does this mean nothing?”

Poor Maria even paid Lanwall (photocopier company mentioned in previous story) every penny they demanded for four years, so even that was all paid up. She did that to protect her credit rating.

So, she wanted to know, how do they work it out?

The answer is, it varies. Companies use their own formulae when calculating a credit score they also set different thresholds for accepting an application. These thresholds can vary according to the type of credit you want, so you could be accepted for an overdraft or mobile phone account, but have a request for a car loan refused.

At any rate, Maria can check her credit rating for free with both the main credit checking agencies in this market: Experian and Equifax. They will give her a free check for a certain period (then she should quit the scheme).

A lot of different factors may apply: perhaps Maria wound up with a zero rating precisely because she has no debts at all! And I hate to say this, but Maria also needs to look at whether someone has stolen her identity and racked up debts in her name, because that is what happened to me. My local MP knew the bosses of the credit checking companies and got me my good name back.

Other points for everyone to consider: Where do you get your grocery supplies? Have you ever ‘defaulted’ through some stupid glitch via your bank? It’s astonishing what tiny misunderstandings may sometimes result in a screw-up.

Advice for all of you: if, when you check your credit rating, you notice an error, you should write to the agency and request that it be changed. If the agency agrees, it should quickly change the file, though sometimes you’ll need to talk to the company that originally filed the data. Also check if the error appears on the other agency’s records, too.

Sometimes it may refuse to amend your file. If this happens, then you’re entitled to add your own comments as a ‘notice of correction’. This will often mean your credit applications take longer, but it may help you to obtain better deals. You can also make a complaint to the Financial Ombudsman.