Hi Donkey I'm off to Poundland ASAP, don't even know where the local one is, might send SWMBO as she likes that sort of operation.
On this sort of thing, about 37 years ago I bought a cheap socket set which was (is still) OK, but the blow molded insert looked kind of flimsy so I took it out and filled the back with a lot of wet plaster with added foam for lightness. The liner is still like new. Now a days the boxes seem to be two plastic mouldings glued together, with moulded catches that break off .
Frank