Without doubt you want The Reefshack mate, in Sittingbourne, Kent. Last week I popped in and met a guy from Bromley, a guy from Surrey and a bloke who had caught the train from Southampton to go and pick up some stuff. The week before I was chatting to a guy who is setting up a 5m x 3m x 2m tank from Shropshire and apparently 2 guys made the treck from The Isle of Wight last week just to shop there. I'm not big on my corals but apparently he has the biggest LPS collection in the South? Loads of frags from £10. I took some pics there the other week and posted them, here's a link
The Reefshack