The old black plates with silver numbers are now illegal, except on cars manufactured before the reflective plates were introduced.
Same as in Holland. I believe the year is 1974, untill then you are allowed to carry the old Dutch plates; dark blue with white lettering. I guess the British law should be quite simular.
In the UK vehicles constructed before 1.1.1973 may display traditional style “black and white” plates i.e. white, silver or grey characters on a black plate. That is unless you drive a Veyron.