For your reference all in one place, a summary of British wiring color codes ("colour" is the usual British spelling).
Note that the hot wire is officially called line or phase, colloquially known as "live." Ground is called "earth."
Original color code:
Live=red, neutral=black, earth=green
For 3-phase, original phase colors were:
Ph A=red, B=white, C=blue.
In 1965 this became:
Ph A=red, B=yellow, C=blue.
In accordance with comon European standards, flexible appliance cords adopted a new system from 1970:
Live=brown, neutral=blue, earth=green/yellow.
Fixed cables stayed the same, until a few years ago when green was replaced with green/yellow for earth.
Where "twin & earth" cable is used for a switch drop, the black is used for the switched live to the light. "Code" requires that the black be marked wit red tape at each end when used in this way, although this is frequently not done.