They are just the name for dealers who are based in London (or possibly other large cities) but have figured out that there's money to be made in the provinces. They send teams out to loads of different towns.
So most of the dealers in Norwich were county lines. In general their product is shittier, they use addicts and minors to shot, usually a revolving door. At least the dealers in Leeds were from the area and you generally had the same few shotters all the time and though they were young they weren't that young.
My guess is that in places like Norwich prior to the London folks setting up there was no way you could score 24/7 so people who did have habits wouldn't have the scope to get as bad, so wouldn't need to do so much grafting to support them. But now you have so many dealers, like once the police coordinated 20 doors going in at once and I did not even notice as a user, maybe had to call 1 or 2 more numbers before someone picked up, people's habits can escalate further just cos of the availability.
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) that they're now trying to verify as to whether or not they actually took place! 
www.nme.com
