MK stuff has been going downhill for many years never really used their accessories since they produced the sockets with the twist shutter. I'm sure in the late 80's there was an NHS HTM issued on them stopping there use on health premises.
In the 1960's some of their output was assembled by home workers one of my relatives lived near the factory in Edmonton and when visiting them we quite often went to the factory to collect a box of plug top parts for assembly at home, I vaguely remember they paid 2d or 3d per plug top assembled and each box had parts for 1000 plug tops