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Yep, Kempie's correct there, I know that much. People are still awarded the ISM (but not the ISO, I think), and this guy got his after 26 years in the post office.
What is interesting is that he was in the Home Guard, but his daughters joke that he hardly ever went on duty with his unit. I rather think that if this was the case then he'd have been kicked out, unless he was allowed to miss patrol on account of his Post Office duties (reserved occupation).