Thanks all, I will get a filter for him - there are some pretty cheap-ish ones on amazon. The tenant is friends with the landlord, and the landlord has been round but of course there was no smoking on that day so nothing for him to be concerned about. He's said he will come any time but needs 24 hours notice at least, which of course isn't ever going to allow him to experience it first hand. As to the stealing, they denied it, I put up cameras, their landlord had builders in who cut the wires, which they denied. It's tiresome and it's not healthy. I hope the filter will help and I will get the police to visit, visibly.