Address smoke infiltration in house from neighbour

The issue is that neighbour's cigarette smoke infiltrates our house. We smell it in the hallway near the fusebox and also in two of the front bedrooms upstairs. We feel it might be entering under floorboards or were wires were drilled into wall. They are both old houses. It is definitely an interior issue. The smoke is coming from inside the neighbour's house, not the garden or anything like that.