Penetrating Damp problem

Hi all I wonder if you can help me,
I moved into an old (1907) house 6 months ago and started renovating recently and discovered previously repaired plaster that is damp (which was removed also the rotten skirting boards) running the length of my side wall.
On investigation I discovered the neighbours entrance path is roughly 2-4 brick courses above my blue brick DPC (not there fault as such ..they just moved in also).





my questions are :-
1. What can i do to repair the damage internally or externally?
2. If it's a major job externally ..who pays the bill?
3. any recommendations for the repair in the Midlands area?

many thanks in advance

Jake

What is going on here:

next door having it replaced

In that case, wait.

Although the path being above the DPC is certainly not ideal and is a possible cause of the internal dampness, if that downpipe/gutter is defective, thousands of litres of water will have been pouring on that path and inevitably finding it's way into your property.

If you still want to fix the path being above the DPM, one way would involve removing the section of it against the wall, forming a drainage channel below the DPC level, and fitting a raised kerb or flush metal grating at path level.
However this will involve significant cost, probably result in most/all of the path being replaced and might not even be the problem anyway - that path looks to have been there for many years.