I've been based near Leicester for the last few months, and I found a load of blackthorn trees lining a bridleway. I don't know whether it's a north / south thing (as I've only collected sloes in Cumbria prior to this), but I've never seen as many sloes in my life. In places they're almost clustered like grapes, and I've been able to wander along just taking the easy pickings. I've got four bags full in the freezer now, and a busy weekend ahead making sloe gin.