I am making an assumption here, but I would say that a minor scheme would be one with no more than a few dwellings on it. It would certainly not be a large scheme, which is currently designated as more than 10 dwellings, so perhaps one or two houses; no more than that. In fact, it might be just one dwelling.
I can also assure noble Lords that the technical details must be negotiated and agreed before developments can start, so in terms of the rigour of the planning process, they cannot be agreed afterwards. They have to be agreed before the development can go ahead.