I don't know how things work in the UK, but in the US it's very unlikely that you got busted from visiting a grow shop. Even multiple times. I hang out at my grow shop about once a week, or once every two weeks, and guys roll in there buying 20-40 ballasts, talking about how they are renting out a warehouse to grow in. It's happened at least three times that I can remember, and no one has been busted as a result.
If you spent an obsorbient amount of time on 420 sites, they would need to have an investigation open on you BEFORE you went to those sites for that to mean anything. Even at that they would need more information, more evidence before they busted down your door.
So if you don't think the neighbors smelled anything, and you don't think you got "grassed up" (i don't know what you mean by that), it sounds to me like you need to do some investigation and find out what's up, because you got caught somehow, and it wasn't through the grow shop or the internet. My guess would be a buddy ratted you out.