I think I have spoken to Dr. D in the fairly recent past - I'll see if I have a phone number or email.
Of note perhaps, when we were on our trip back from Paris on 5 May 1963 in the Proctor we popped in to Persan-Beaumont. I noted F-BCDU, Magister c/n 850, the plate read Philips & Powis Reading. Also Miles 'H.T.3' F-BDPG c/n 1783. Whether my abbreviation, or actually shown on the aircraft I can't quite remember.................!
I also own a Biro....
Who designed the peculiar front glazing on, for example, 'EEG? Was it particular to Miles' products? I recall seeing Lord Montgomery one day near Farnborough, and his car had a similar backward top to bottom sloping windscreen.