Yes ... well ... I volunteered once ...
As a young officer reading the Station Routine Orders in the 1960s, I received regular invitations to volunteer for the injections. Once, when I had some exam or other to prepare for, I popped round to P2 to book in. I was usually quite trusting in those days.
As it happened, the Chief Clerk was standing by the desk when I hoved up. I had known this very senior figure to treat me with most amiable respect until then. So I was startled to have him cut me short as soon as I explained to the P2 clerk why I was there.
“A young gentleman like you does not want to concern himself with such things … Sir !” One did not ignore a hint put so forcefully by such a figure.
I wonder if, like the German civilians who professed not to know what was happening in Buchenwald, people who mattered in the service at the time knew the Porton holiday to be more dodgy and more dangerous than it was presented to be.