Broccoli of any colour is a fairly recent introduction to the UK. In the last series of 'Call the Midwife', the midwives and sisters were about to have broccoli with their meal, when someone pointed out that no-one ate broccoli in this country in the early 60s. They went ahead with filming, but used some CGI jiggery-pokery to turn it white, so that it looked like cauliflower.
The information on the Internet about the origins of purple sprouting is conflicting. Some claim that a purple variety was eaten in ancient Rome, but after a wait of centuries, a 19th century Dutchman developed a strain which was exported to the USA, where it took off before we took an interest in it. Naturally enough, another source states that modern purple varieties were first developed by an Englishman.
From my own personal experience, I can state unequivocally that the book
The Vegetable Garden by E.R. Janes* (pub 1954) contains words to the effect that "in late autumn the cauliflower season has come to an end, and we must continue the sequence with broccoli" (whether he meant purple or white, I don't know). However, since the venerable Janes spent most of his working life as head gardener to certain "great country seats", it may be that this pre-60s broccoli was a treat enjoyed by the more privileged classes.
*The tome belonged to my father, and was the first inspiration behind my own desultory experiments on a council allotment.
