Ewoowar - no I think it must be a regular spot as you've just confirmed what I've witnessed in the area on 3-4 occasions and I don't even use the route daily. As I said in my previous post maybe the authorities settle for this as at least they can watch what is going on and it is a relatively safe place.
A lot of kids congregate on Hartham and the vast majority are there to chat with their mates and get out of the house, play sports, etc. - in summer its a great place for them to hang out and play - but inevitably this also brings along the alcohol and drugs (lets face it alcohol is the most anti-social and the biggest killer) for some of the kids. Mine tell me that Hartham is fairly well 'unofficially' sectioned off into year groups and social groups so its all about trusting your kids and their mates. I wouldn't want mine drinking over there under age as there is no control and it makes them vulnerable to society's 'predators' but allow them to have booze at home for their 'gatherings' as otherwise they will find a way and that way may possibly be Hartham. In my teenage years there were plenty of pubs in Hertford that would let me in to drink in a safe and controlled environment - but that's no longer an option for many teenagers with the price of pub drinks and the ID requirements/over 21s rules.
Kate you wait until you get the request for Reading tickets at the end of the GCSEs and plans to go to various summer destinations when they turn 18 after A levels! As horrifying as it sounds, and is, these trips are part of the passage and if your kids go with the right groups you'll find out how they actually use the bonds they form at places like Hartham to look out for each other in these hell holes and from what I've heard the Hertford tours (50+ kids from local schools every July) to the favourite destination of 'Napa' seem to go quite well