Old numberplates for temporary exports?

[geeman237]

Does anyone know the details about the special numberplates that used to be issued in the 1960's for cars bought in the UK by foreign buyers who would drive them about then take them home to avoid import tax? At least I think that was the story behind them. I think they were the yellow background and black lettering ones but they had a special border? I recal a chap in Devon had one on his Herald 13/60 estate. Does anyone know of them being remade by any of the old numberplate reman companies?