In the sixties and seventies, there was a lot of criticism of the impact of AmE from the language conservatives in Britain, who saw it as radical and forcing the rate of change, but you no longer hear them much. Much of that was a result of the massive increase in exposure that went with TV, music, etc. Many do assume that BrE is in some way more authentic as it's the original, though as you say it in many ways less close to the original than AmE. It's also interesting that most of the voices trying to act as a brake are from America as BrE merrily rips the rule book up. Nowadays the British conservatives blame the education system, especially progressive teaching methods, and not America for what they see as a decline in standards.