Just as a related aside to this ... I know there are differing views on black/silver old style plate (I personally like them fo a traditionally styled car like the Morgan) .... if your car is registered as Historic you can legally fit black/silver plates up until 1980 .... after 1980 you need to retain the reflective plates.
So there's few years window when cars early in the use of reflective plates can retrofit the black plates but a cut-off, so that concession doesn't roll on with historic status after 1980 like the tax/mot exemption.
K
