Then you need to give an idea of how much space (sq m) you need in workshop. You won't get change of use permission for typical shop with flat over, and you can't run a commercial machine shop from residential premises. Most small industrial unit won't allow residential use. Your best best bet is a near London small farmhouse with outbuildings. A mate of mine runs a specialist car tuning place and lives next door. He had exactly this problem when looking for premises. Not saying it can't be done but you'll need to find something already doing something similar which might mean buying an existing business.