I have a couple of 1977 crowns in those black Midland Bank pouches illustrated by Mackie. They (the coins and pouches) are still apparently in the same condition as in 1977 despite having lived at least 23 years of their life in rather damp houses. The same goes for similar, but entirely clear, pouches from Midland and other banks housing 1980 and 1981 crowns.
I suspect the hard plastic carrier was available for a premium or was provided by a third party giving away coins as a promotion for something. The official method of issuing these seems to have changed over the years - the 1951 Festival of Britain crown came in a cardboard box*, the 1953 coronation issue was in a rigid plastic container like the lower one in Mackie's picture, and the 1970s/80s ones in pouches. By 1990 when the first £5 'crown' was issued, they'd abandoned any form of packaging, and by the middle of the last decade they'd abandoned issuing 'crowns' at face in banks at all.
* Off-topic, but can anyone enlighten me as to the difference (apart from the obvious) between the green and purple boxes for these? I have a green one, but I've seen purple ones and the coin doesn't look any different.
