Regrettably, as vile as I generally find tobacco smoke, I doubt if you can get anyone to apply pressure beyond what you yourself can generate on the housing trust whose property it is. Unfortunately, housing quality in the UK is frequently not good enough to prevent the experience you have had - we live in a Victorian building where there are 60cm (two feet or so) of stone, soil and general rubble making the wall between our bedroom and that of next door. We occasionally smell the neighbour's cigarettes in our bedroom. This problem has thus been going on for at least 130 years - not that that is much consolation to you. There is no legal requirement of anyone to stop it continuing, else more or less all housing stock in the UK (apart from completely detached dwellings) would be due for an appropriate overhaul. I suggest you petition the trust and get statements from all other residents in your complex who have the same complaint. As you describe it, this is a soluble problem: install a fan near the top/terminal of the conduit and run it continuously to ensure no back-flow can occur.