IMHO, Chalgrove is used for much more than the Meatboxes. All 0/0 and slow speed testing is done there on the airfield by a large seat test department. It has Cartridge production and extensive storage facilities on site. As for the F35 testing in France? It's probably because The weather there is much better for high altitude testing and the test area (Caseaux) is much bigger and restriction free.
However...There are a couple of 'new' alternate routes for the proposed Oxford to Cambridge Expressway which pass either side of the airfield. I suspect the OCC's little eyes light up when they think of a 5000 home development next to a new motorway
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Just my personal opinion of course!