I am coming around to that, although maybe not until next summer due to all the clutter in my house which will make it harder. Meanwhile, the 'garage board' workaround could hopefully enable me to replace my boiler soon rather than risking it fail during the winter. Last weekend, a very helpful electrician who had been rewiring a nearby house, I suspect one of the first on the estate to be rewired, also considered that it was a grey area, and importantly indicated that he knew an electrician who would probably be able do it.
Having confirmed the facts, it really does seem disproportionate that the the introduction of the 18th Edition Regs meant that overnight simple jobs that could be previously be signed-off easily could, when green gue was present as it will be in many properties constructed in the 1960s, only be signed-off after a full rewire.
Surely overreach: while modern installations undoubtedly provide more protection, there don't seem to be many cases of people actually suffering harm, relative to risks in other everyday activities. And as far as I know, there are no campaigns encouraging householders to upgrade their electrics, no date set by which old fuse boxes must be replaced, and equally no requirement for properties' electrics to be tested periodically - say every ten years - to ensure that they are safe.
In my case, although not a taxpayer, and losing my winter fuel allowance, having lived very frugally for many years ultimately I can afford to have my house rewired if necessary, although it's a lot of money.
Thank you all for the advice!