"a campaign to put razor blades under the flaps of letters"

That I find difficult to believe. In his book "Bureaucrats and how to annoy them" (published under the pseudonym R.T.Fishall) he is quite emphatically against anything illegal.

He seems to have been the sort of gentleman who could strongly hold a minority view, and present it without forcing it on those who didn't happen to share it.

BTW, please don't confuse nationalism with racism.