Since this is all in the same territory, Legal Girl, I hope you don't mind if I answer Factor on your thread.
Firstly, the problem when you come to sell, although real, could be only "technical".
To look on the black side, you know it's a legal requirement to notify Building Control and have the necessary inspections etc. A buyer could rightly ask for (to use the jargon) ...... regularisation.
Some lawyers would argue that 22 years makes it "historic", and disregard the potential problem. I know this is often the case where 30 or 40 years have lapsed.
Unlike Planning (crudely ......... after 4 years, they can't touch you), Building Regs have no official "statute of limitations".
For peace of mind now, you could apply for retrospective Building Regs Approval. Unless you're very unlucky, you should find the BC Officer sympathetic. Assuming there are no glaring breaches, and the work is still sound after 22 years, it shouldn't be onerous.
The BC Officer won't be looking to "come down on you", but he may find contraventions that he may be unable to ignore. It is possible that some remedial work may be needed.
It's a difficult call. Either to keep quiet, or resolve it completely, but maybe at some cost.
Providing that BC have absolutely no knowledge of this, you could wait until sale time. If the anomaly is picked up then, there are Indemnity Insurances available. These are used all the time now. The Insurance Companies love them since they very, very rarely have to pay out ......... easy money ;o)
A one-off payment of £100-200, and everybody's happy.
It would help to have an experienced builder, or surveyor to go over the work with you. They may well tell you to go for retrospective.
I wish I could make the decision for you :o)