What I'm now mulling over is, if I was to commission a structural
survey now which would hopefully confirm that 10 years on, the
building is perfectly sound; together with the above certificate which
presumably guarantees the underpinning work carried out; wouldn't this
serve to convince any prospective buyers that there wasn't a problem?
Or am I nuts even to be considering this?

(I do appreciate there could be problems with obtaining insurance; I'm
looking into that issue separately.)

I live in a bungalow that was underpinned before I bought it. The work was
done under the supervision of a firm that are still in business and who were
most helpful in providing details. The sole problem I have encountered has
been the reluctance of many insurers to take the business. If you can get
that sorted out then fine. Otherwise walk away!