SMGL-3058 British & Nazi Examined Envelope

An interesting envelope you don’t see too often. Looks like the letter (not included) was examined, placed in the envelope, examiner 612 sticker added, address written, postal marked in London, then intercepted by Nazis (or maybe they had a deal with Switzerland to inspect mail?), inspected and resealed and Nazi stamped again. Wow! lol I wonder what was in the letter? All we have is the envelope. Very neat.