Without going into loads of detail, and foregoing a few ifs and buts for the moment, it sounds like the last use may have been sui generis (no use class) or B8 (storage) and that a B2 use would need permission. Having said that, the proposed activity doesn't sound like a B2 use per se and it isn't a B8 storage or distribution use, so it will need planning permission (with an exception I'll come to). What you seem to be proposing is a waste sorting/recycling facility - I've seen these described as Class B1c (light industrial) and sui generis (no use class) in different planning authorities. This could be down to inconsistency (it does exist!), or a hybrid of storage use and industrial process (eg. sorting) that may warrant a sui generis tag. To fall within Class B1 the use needs to be one that "can be carried out in any residential area without detriment to the amenity of that area by reason of noise, vibration, smell, fumes, smoke, soot, ash, dust or grit." Any industrial use not meeting this proviso is going to fall in Class B2. The proviso on the change of use is that B8 to B1 doesn't need permission where less than 235sqm of floorspace is involved. This is such a small figure where Class B uses are concerned that I've rarely seen it come in handy.
