Robin wrote:

I think it may depend on just what you mean by "structure and integrity".
Eg if you need evidence that the blocks and mortar were appropriate/to
specification then I think you can't get away without samples.

Yes, that makes sense; thanks.

If this is part of your long-running neighbour dispute I think you need to
be guided by a surveyor.

I'm afraid it is, and I have been (and still am). It's complicated and I
don't really want to go into details here, but it concerns alleged damage
which (again allegedly) can only be assessed from my side. I was wondering
about possible alternatives to stripping away plaster should things ever
come to that.

Thanks to you and everyone else for the thoughts.