Not disagreeing with JF, since what he says is the practical answer.
The theoretical answer would be based on
CAP632 - see Ch4 and the Harrier for all sorts of reasons would be a "Complex" type. All* current UK ex-Mil Jets are 'Intermediate' (JPs, Hunters etc.). 'Complex' types have a high hurdle of engineering support, in principle equivalent to "manufacturers' support", in order to get a Permit to Fly.
NoD
* The Vulcan is an exception - there may be the odd other. A degree of the problems in operating the Vulcan are the costs and procedures involved in requiring MA as a design ? maint ? support? organisation.