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Well. I have no idea what has happened in this case, but pieces of land in conservation areas can be worth considerably more if something unfortunate happens to the existing structure. One problem with conservation areas is that if the protection against demolition provided by the conservation area falls away, there is often no local planning guidance to fall back on to assess future planning applications. I've seen a lot of nasty things happen around that.
(For all I know, no such suspicion may be appropriate here and the collapse may be quite innocent.)
That feeling when your house collapses and it's in a conservation area and you didn't have planning permission yet.