As NigeF rightly says it has the look of cavity bridging. I wouldnt think its a solid wall as suggested as there is block internally and brick externally. I would suggest clearing out the rubble by the wall externally, next time it rains heavy go outside and check if the guttering is working properly (you may have water running down that wall from the guttering corner above). Then if all else fails remove a brick outside the damp patch and see what is hidden behind.
Difficult to get a sense of scale from the photos.
Easiest way to tell if you have a cavity wall is go find an external door, perferably on the same wall and measure the distance from the internal side to the external face. If it is about 230mm then it may well be solid, if its 250mm-350mm then its most likely cavity.
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