What's on the outside?
If there are vegetation or soil these might have bridged the dampproof. try clearing them away from the wall. If it's just soil, dig down 2 course of bricks and fill with large gravels to aid drainage.
Some tenents are just plain stupid. I have one woman who rent my 1st floor flat in a block, been in there since last spring, before x'mas she complained of damp in her bedroom, when I went to have a look, yes the windows and corner below the window is crawling with mould. She insisted there are damp, I tried to explain to her it ain't rising damp (if it was ground floor flat would be swimming in it), not penetrative damp (outside wall dry as bone and no evidence of leaky gutter). I explained to her it is basicly condensation because she doesn't open the windows and her bedroom has the largest outside wall which means it's coldest part of the flat, moist air condensed on cold walls, it hasn't help she dries her clothes on a rack inside the flat. I'd bought her a dehumidifier just to preserve the peace, but told her in no uncertainty terms she mustn't dry clothes indoor. Went back last month to check, guess what she still dries clothes on the rack indoor.