The Flag cell was the usual large capacity type used for bells. Seems it eventually gained a more conventional number, R40:
https://www.vintage-radio.net/forum/...7&d=1334951107
Interesting that the relatively modern plastic-cased version there was made in Denmark, not somewhere I've noticed before in connection with Ever Ready manufacture. I bought one or two Flags in the late '60s, and last saw new examples at my first workplace in the early '80s: I can't remember what we used them for there.