The comic pre-dates the ban, but that doesn't mean the stamp on it does. It could have been applied long after, as the T&P stamps clearly were on the 1958 dated Charltons.
Let's not forget that T&P were the "sole distributors in the UK", and the UK comprised England, Scotland, Wales and NI. So the books they imported should have been distributed to NI too, if we assume full UK distribution. That to me makes the other stamps for somewhere else, and the obvious place is Southern Ireland.
I'm going to let you and Robot battle this one out as I'm knee deep in Charlton, Harvey, IW and Murray at present