Did Miles and Mingus do 'Anglo'? 
The first definite connection I recall reading concerning Miles was with Paul Stuart; toward the end of the 50s; perhaps when he was first making big money.  I've no idea what he might have been wearing as a youngster, kicking around with Bird, but Miles was hardly blue collar so maybe Davis Senior had something to hurl in his direction. 
Later, apparently, it was full-on Italian (cashmere?), but about this 'soft English tailoring'.  Was it something being done/offered/taken up in and around New York?  Or did Miles fly to London for consultations?  Were the jackets padded?  One presumes not (but one only presumes).  Were the shoes English? 
I like the sound of it all but have no answers.
The Mingus thing comes across as a wry joke on his part.