Say, Junkman, where were those photos taken? Usually, I can identify Sixties U.K./'Commonwealth' license plates, but those black ones, surprisingly, I've never seen before.
All UK registration plates were black with silver or white fonts until 1968, when the reflective black on yellow (rear) and black on white (front) plates could be fitted optionally to all vehicles. They became mandatory on new vehicles in 1973, with the exception of buses. Pre 1968 vehicles never had to be updated with the new style ones, but many owners opted to do so. Since 2014, all vehicles registered as historic, i.e. 40 years or older, are allowed to be fitted with the old style black plates regardless, even if they are built after 1973. The intention was to allow owners of imported classics to fit their vehicles with period correct plates, but they forgot to specify the 1973 cut off date.
Ah, very good! I really had never seen the 1960s plates, only period-correct ones from the 1930s-1940s, in certain shows exported to the U.S. Well, now I know!