You can buy chimney balloons to stop draughts from coming down chimneys. I got one for my old flat to stop the pigeons kicking twigs and dust down from their nest on-top, it worked a treat and would certainly help with any smells from a shared chimney as you'd just be sealing your part.
Ring the police, say you're going round next doors with a shotgun and intend to shoot the lot of 'em How did they burn toast quick enough? I'd just keep calling
If you can get some evidence of it, especially of approaching them and their "comments" back, then that may help on the side of a criminal behaviour order, that may help with the council moving them potentially if they are in council housing. I would also say to see if you can get any plain clothes cops into your house as "guests." If they can smell it, they'll have them I reckon. Just a few things I've learnt over the years off my old man, who actually is a solicitor. It's all about getting some foolproof evidence on either their behaviour or them smoking. Police, or a "friend" shall we say, backing it up is the icing on the cake.
That's funny On topic though sounds like you could do with one of these when they come out. http://www.hightimes.com/read/stonerproblems-marijuana-detection-device-coming-2015 The idea of getting some plain clothed coppers round though, is a pretty good idea especially if you know the times that they smoke it, and then get them round at that time so they can then inform others to come in a marked car or they go round. Be prepared for a long battle though, it took my uncle nearly 4 years to get his neighbours out for excessively smoking weed and he had to send my cousins to live with my nan, until they were gone. Whilst I don't have a problem with people smoking it, there are people who just take the biscuit when doing it which is what sounds like what you have. Make sure if you are getting headaches etc that you see a doctor and get it recorded.
Move out for a few weeks. Before you leave, turn your stereo on full blast with Rick Astley's Never Gonna Give You Up on a repeating loop. When you return you may find your neighbours much more amenable to the concept of peaceful coexistence.
Knowing my luck they are probably huge fans! I spoke with the housing officer today and it has become clear we are not the only neighbor that has had complaints. They have repeatedly broken the terms of the agreement and face eviction. I know of several instances that has got them into bother. 1 was smashing the front living room window , and another was with the teenage son be verbally abusive in the street. I just hope they are gone before I sell I still think leaving an open tin of Surströmming near the vents over the weekend is fair justice
If its so strong its coming through the walls you have a structural problem, or there growing. My friends house had this same problem with heavy *** smokers. It came through the floor boards of the house. the brick between levels must be thinner or broken. They ended up moving out because of it.
Have you got shared loft space? i know in my other half's house she shares the loft and the space under her living room floor with next door.
Well I'm pleased to say that so far things have been fine. I blew my top and went around there a few weeks ago and kicked off! 2 lads came out and immediately started to size me up! I must have looked and sounded like a nutter because they soon backed off Anyway after a final warning from Teign housing and a police visit there have been no problems at all and our house smells nice and fresh when we get home. Maybe they gave up the habbit or just smoke outside? but either way I'm happy
Maybe they swapped to something not so whiffy! Or maybe you're the "odd" neighbour that might knife them in their sleep now..