Round recessed schuko outlets fitted into skirtings and wooden panelling seem to start appearing from the 1930s onwards.
BS546 (mostly the 15A variety) seems to start appearing in the 50s and then abruptly disappears again, but quite a lot of the 1950s rural electrification era houses had BS546 fittings.
After that BS1363 has pretty much rulled the roost eventually becoming IS401 (Plug) IS411 (Socket)
I think the logic of moving to BS1363 rather than Schuko was to remove the mixture of earthed/unearthed outlets and odd combinations of schuko plugs being inserted into old BS outlets (bypassing earthing)
Square pins were nice and incompatable!
