Freddie still lives in UK but doubt he will answer the question of the 'Shepherd'.
I knew him when he had just left the RAF as a National Service pilot. He started as a reporter for the Kings Lynn News and Advertiser and we both used the same pub, on the corner of the square, in Kings Lynn, Norfolk.
I recall his interest in RAF Marham, where I was stationed, as it was the Valiant nuclear bomb facility...he had a nose for journalism and constantly asked me about things going-on at the base which, I confess, I wasn't aware.
However, I probably made up some typical RAF B/S just to flow our conversations, depending on how many pints of bitter I'd imbibed...it's possible he even included my stories (crap) in his books!
That's why they are fictional...