Here is is legal to purchase, and to grow for personal use.
I think the new varieties of the plants are much stronger smelling than in the 70's. It can be smoked in public much like cigarettes, away from entrances or restaurants. I agree it stinks.
There is a different smell from growing it to smoking it, a skunky smell. (I just realized you don't have skunks in the British Isles). The plants are quite strong smelling, and those that are serious about their plants will have fans to ventilate the smell from either greenhouse or growlight area of their home. We have someone in the neighbourhood growing and I can smell it when I step outside sometimes. Maybe it's just when the oils in the leaves are stronger when the plant is ready to harvest that it smells, because it is not all the time.
You can ask your neighbour to smoke away from windows, or even get a fan to blow it the other direction. Good luck.