Damp inside wall on Victorian end of terrace house

[Mike BD]

We have an end of terrace Victorian house that has a sloping service alley up the right hand side. Our ground floor lounge has damp issues on the wall adjoining the alley. The issue seems to be the alley slopes from the road and bu the back of the lounge the alley surface is about 1500mm above the floor level of the lounge. What would be a good solution to stop the damp? Does the alley need to be dug down to the floor level of the lounge? Would damp proofing with a sheet DPM on the inside wall of the lounge then correct the issue? I am advised that stopping the damp on the inside would only cause the damp to go around the DPM layer and come in somewhere else? Please advise. Regards Mike BD

[newshound]

I certainly agree that you should block the damp at the outside, not the inside!