Why were so many British films of this era in black + white?

This may be a really stupid question, but for some reason it's only just now occurred to me to ask it. Many of my favorite films are from the postwar British period in the 60s (there are many others from the 40s and 50s but I'll leave them out of the color argument.) Examples: A Taste of Honey, The Knack and How to Get It, Loneliness of the Long Distance Runner, Accident, The Servant, King & Country, Victim, Bunny Lake is Missing, etc. I imagine it must have been a stylistic choice as color film was available then, and the lack of color became part of the characteristic style and mood of these films. Was it a sort of unspoken, collective aesthetic decision by directors working in Britain in the 60s, or part of a school of film?

Antonioni made Blow-up during this period and it clearly didn't belong - it came out in stunning color. It almost makes his film seem to belong to a different era. Modesty Blaise was bursting with color (unlike Losey's other films mentioned above.)

There must have been many intelligent things said about this period and style of filmmaking - would someone enlighten me as to where to read more about it?