Thank you Peter for a very clear answer. Translated into Germanit would be a very good answer for anyone over here with the same problem.
Here a weapon can now only be deactivated by a gunsmith and must afterwards be checked and marked by a governmental agency. Which, with transport to and from the agency by approved means, plus the cost of the "negative proof" on top of the gunsmith's work, makes it so expensive that a "modern-rules" de-act is more expensive than a perfectly usable functioning weapon. The result is that new de-acts are uneconomical for dealers, and have become extremely scarce, and many old rifles are simply scrapped outright, not even being available for parting-out. So "old-rules" de-acts are at a premium! Has the market in the UKbeen affected in a similar way?