An architect friend has advised me that my cavity may be 'bridged' or filled with debris possibly brick ends, sand and mortar, all possibly dropped by the 'Brickies' during construction, 1960s ex-council house causing damp problems and effectively creating a 'single-glazed' brick wall. The neighbour's wall in the passageway has been done more than likely as two bricks have been removed above the damp course by the housing association. Also suspect poor cavity insulation job in the walls as house is cold but not sure if this includes the passageway wall on the ground.