Where I lived previously there was a field behind my house that they built new houses on and the first thing they did was take all the topsoil away in hundreds of lorry loads. They scrape it down a few feet until the hard soil is reached. That was a field which was always crops except one year they had sheep in it over a 36 year period. I assume it would be good quality with very little broken glass etc.
There will be building sites though that were maybe previously waste ground that could have lots of rubbish in it. It will all be sieved no doubt but possibly some will get through.
There will be firms who buy that topsoil then process it and supply places like Homebase, Wickes, B&Q etc possibly with the very same soil but just in different bags. There's a potato factory near me and they supply the likes of Tesco, Morrisons and Asda with the same spuds but in each firm's own bags and people actually say oh Tesco's ones are far better than Asda's ones
