There's no such thing as a universal credit score/rating, per se. The information recorded is about the type and amount of credit offered, and your payment (or otherwise) history, and from that they can make decisions on whether to accept you as a customer.You are a fountain of knowledge, Gavin.
I wonder if I have a bad credit rating, or bad credit 'score' as you mentioned. About a month ago I applied for an All Saints credit card; I didn't even want to use it, I just wanted it in my wallet to look posh, but they told me my application had been declined (I also later learned that they're supposed to warn you that if it fails it will go against your credit rating - they didn't warn me of this, otherwise I'd never have signed up!)
I'm guessing that your credit history is based on how often you make payments into your credit cards and overdraft accounts? A month ago I had an overdraft of around £1000 and my credit card has at least £200 on it for the last two years - I always pay into it every month, but only cleared 100% of the balance last month; so I imagine I have a bad credit history, even though I've only had £1500 of loaned money, which I don't see as that much?
Each lender or credit institution applies the information towards their own criteria of who is an acceptable customer to lend or give credit to. Surprisingly for most, they're not always seeking those with pristine records.
For example, some credit card companies may reject you for always repaying cards in full, because they won't necessarily realise a return on providing you this type of service.
In order to maximise the amount of credit you can get (as long as you take into account the potential pitfalls of this), you should first gain an understanding of what the banks know about you, can find out about you, and what they aren't interested in or have no access to.
Importantly, you can peruse your Experian credit file (the information made available to lenders) at any time. It costs a few quid, but searching for your own results will NOT leave a footprint on your record in the same way that a third party check will.
Have a read of this
http://www.moneysavingexpert.com/loans/ ... edit-score
and hopefully it will clarify some of what I've said.