Number plates, black and white style on classic car

I thought I read somewhere that it's now legal to use black and white old style plates on cars newer than 1 January, 1973, maybe once the car reaches the tax free status at 40 yrs old?

Period number plate change

I've heard people say that the use of old-style non-reflective numberplates has been extended to all vehicles that qualify for Historic Vehicle class, therefore to to those built before Jan 1st, 1975 rather...