The Direct Debit Guarantee ("DDG")

I am currently working on an article about this, and I could do with some help.

Having been employed as a banker when the direct debit scheme was introduced , I thought that I knew what the DDG was. It looks like I was wrong. ( I was only a novice law student then).

Far from being a "no-quibble" assurance to bank customers that they were guaranteed an immediate refund of any individual debit that they wished to challenge, the actual position is, as I currently understand it, a bit of a "con". The guarantee does offer an immediate refund, but only if an error has occurred. To be fair, it seems that many bankers will in practice not seek to be satisfied that an error has occurred, but many others do.

Given the wording of the DDG, it does not seem unreasonable to me that they should require some evidence that an error has really occurred. However, to the extent that they do, it will inevitably make the "immediate" refund impossible at least as often as not.

Or am I wrong ?