I had the same problem with the neighbour directly below me in my small block .
The previous occupants never opened their kitchen window as they have air con in there -- the new occupants just open the widow .
Another cause of smells drifting up is if the offending flat has had a hob hood fitted over the cooker and as it's a fan extraction it could be blowing the smells directly up to you
Eliko -- at a guess I would say that Sotos lives on the third floor if the smelly ones are on the first floor and there are two floors difference.
Sotos ---- at least if you get on ok with them you know when it's the right time to pop in for a coffee
Bill