...the little blighters seem to be happily camped out in one area of one wall, you see them heading into cracks in the brickwork - thankfully none have made it inside (yet!!) - ant powder sees them exiting pretty sharpish but they seem to keep finding a way in/out. Solid walls (1920s) AFAIK, no cavity as such.
Anyone got any experience of tackling this? Obviously a lot on the internet already but there's usually at least one voice of reason on here that can cut through the myriad of supposedly de facto solutions