I think you've got to get up and look at the slates in the area. You may have a leak onto the top of the wall (under the slates). Water will then find its way down between the bricks.
I see mate. Wondered about that and asked the roofer that I've had doing the repair work today to see if it was getting behind the guttering and running down the adjacent wall. He said roof felt and such is in good nick. Said he's pulled some of the tiles forward to overhang the guttering properly on the corner, so maybe this could have been causing it? Would be the right location to be fair, new staining that I can't attribute to a previous leak is around the corner.
Me and heights don't mix, so will have to get a mate to look, although as long as the roofers done his job he should have identified this as the issue and sorted it.
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