"The current styles of "British folk guitar" are derived from the revival. "

That's certainly true but there have been a number of people since then who have had a major influence on the way the guitar is used in British folk music. The first, of course, has to be Davey Graham and the introduction of DADGAD tuning. The second , I would say (but this is only a personal opinion),is Martin Simpson, using a variety of tunings, blues riffs and slide. You could also argue for Martin Carthy and a number of others but there is much more variety of playing and, generally, a far better standard than I remember when I first got into folk in the mid 60s.