The wholesaler I use has a "Trade only" policy, and the signs outside their warehouse say that. (They're hidden away at the end of a dead-end road on an industrial estate, so only people who already know of their existance are likely to roll up at their door anyway.)
I don't know what it's like in their other branches around England, but the manager here certainly interprets "trade" fairly liberally. I've been in there when owners of local hotels, bars, and so on are ordering materials, and they clearly aren't quite sure what they need.
