Ilmiont
As you're in Oxfordshire had you looked at what Silverstone has to offer? Probably not the complete package you're looking for in one day but they do a variety of experiences like skid pan, performance cars, single seaters and track days at reasonable cost, you might well end up doing a few days and then having to put together the bits you learn.
silverstone.co.uk/drive
Your approach of trying to find some good tuition is to be applauded, there's a lot of us old farts here who can be a bit huffy about careful driving, but I for one will admit much of my ability has unfortunately come from getting into sticky situations on the road and learning from them, and with millions of miles in cars, vans and trucks I still find myself learning little bits here and there.