I've read about MUSTARD before, and seen it described as another Miles M.52... in that in the 'spirit of cooperation' it was shared with the US, who once they had the plans suddenly found that what they had was too secret to be shared. The Miles M.52, of course, looks very much like the
Bell X-1, which went on to break the sound barrier for the first time.
MUSTARD fate's was apparently similar, though I'd love to learn more from those in the know. Some of us would know it as the Space Shuttle.
Anyway, its designer has just died, RIP:
Tom Smith - Telegraph
Why 'the other TSR.2?' Well, just another aerospace project where we were once so far in the lead...