sound like a typical old stock wall allowing damp to soak through. Best long term solution would be to fix external grade ply to the wall and cover in Lead. Expensive but very good.
I just wonder if planning would have anything to say re adding lead topped ply copings or indeed stone or man made stone copings?
Surely not, but I'm sure a lot of us have come up against their intransigence.
One thought, could a run of roof matching, sufficiently wide slate be affixed to the protruding masonry??
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