The U.S. official praised the contribution of the newly-trained British crews. He also noted that the UK had been given “unprecedented and total” access to the highly classified SIGINT systems on the Rivet Joint.
Stuff the SIGINT systems, I reckon it'll be the total lack of access to design and qualification data for the airframe that's got the MAA's back up.
The only way you could satisfy today's post Hadden Cave airworthiness requirements is to start with a modern design not one that started out life on a 1940's drawing board.