Thanks again Nick,
You are very helpful.
(Incidentally, I was amazed when the cylinder split open ... "Indoor water feature" ... nice!)
The wall does seem thick .. more that a brick plus mortar.
Separate issue in same room.
See photo of kitchen sink - same bloody kitchen!
There is clear damp here. I wonder is it straightforward??
Is it just because water got under the tiles at point "A" - near the coke can??
Is it rising damp from that??