Going back to the original question, I understand the last A-B coinbox was removed from the Isle of Rum in the inner Hebrides, possibly in 1994. Apparently it went straight to a museum somewhere. This information came in 1995 from a stallholder selling antique phones and a decimal-converted A-B box, who told me that the last one was removed a few months earlier.
There is a web page
here which shows the later version in use in 1994. Certainly I remember the later model, often with a separate 700 series handset, was quite common until the late 1980s. The earlier version is described
here.
It seems there were a lot of dishonest people about. I often used to see vandalised payphones with the coinboxes ripped out. I suppose it was seen as a victimless crime, since the phones were owned by the government, then BT who were seen as a huge faceless company making vast profits.