I didn't know there were 90,000 men in a Panzer Division. When I was a boy, Nazi Panzer Division had more like 14,000 men. (U.S. divisions had about 16,000 but slightly less firepower on paper because of fewer automatic weapons. Of course U.S. Divisions were a lot more likely to have their full complement of men and equipment.)
An NYT book review has Ewen Montagu's brother a Soviet spy. It says that Ewen didn't know about his brother but that MI5 did.