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Thanks for that info, I'd never heard of MI9. I've done as you suggested and I'm now looking for books on the subject. I suspect this particular wormhole will be well worth the time.
Helen Fry has written a rather good book about MI9 save for one serious flaw . . . . . . . . . . she said it was disbanded at the end of the war and other sources say 23 SAS took over the role. That is not what I remember from some time passed in a place in Kent and it was still going albeit as small as its original staffing at inception in 40/41 and perhaps in another county now.