...I know this thread is a little old, but I just thought I'd chip in with what i know about the dealing side of things in the UK (which is a fair bit actually... not so much about the growing side of things though... yet anyway!)
Most of this gritweed is being grown by the vietnamese/chinese groups operating in the UK... which so happens to be the types of gangs also involved in other crimes such as people-trafficking, forced labour/prostitution, etc.... which might give you an idea as to how little they care about people's health and well-being generally.
They tend to rent houses for short-term periods, turning the whole property into growing factories (examples of which you may have seen in the news). UK police have started to crack down on them, scanning whole streets using heat-sensitive cameras to detect anomalies that would indicate large-scale growing. The main guys never get caught though, as usually the only occupant is a teenage illegal immigrant kept in to babysit the plants, who couldn't finger the main guy even if he tried.
And the contaminated weed is still just as much in circulation, however they have moved on to different methods of adding weight now, past the initial scam of spraying glass etching solution (i.e the rock hard type of weed) to a whole palette of different contaminants. Some of this weed being offered now can even pass the look/feel test fairly easily... though your nostrils are still a damn good way of passing final judgement imo!
Anyhow, these operations routinely get shut down, thus increasing the demand/price for weed. Alternative sources of good weed are hard to come by too as very few dealers can compete with the quantity of gritweed being grown/sold... you'll find a lot of dealers selling gritweed but keeping a pursey of proper weed to smoke themselves. And if you add this to Gordon Brown's retarded near-zero-tolerance policy to cannabis, you get a pretty solid picture of why things are pretty shit for UK smokers these days...
Anyway, I'll quit ranting/rambling now.... suffice to say, I want the 90's back!