I can't remember where I read it now but there was an article somewhere that said the most important ingredient was the English malt, specifically Maris Otter - and that some brewers don't use any crystal. Or when they do they use MO and a touch of crystal. I have found the British crystal to give a more authentic "British" taste than other crystal malts. I know you just said you aren't interested in what "homebrewers" are using, but to my taste and my experience the Medium British crystal seems to work best in, say, Ordinary Bitter. And Maris Otter, of course.