Damp proof put in on that wall in 1985 by a company called triple treatment..they drilled the walls and filled them ..this has all been covered up now ..they treated the inside too. The walls are plaster .Correct gaz making assumptions here and we know what those do....
Questions for OP (to assist)
1: What is your wall construction? 225 solid brick etc.
2: Does it have a damp proof course to your knowledge? Typically slate in that era. Or has it been treated in the past? With electro osmotic system or chemical DPC?
3: When was that pointing done and crucially is it like or cement?
4: What is the internal finish? Lime plaster? Or cement scud coat? Is there any insulation and if so what is it? Is there drying lining if so provide details.