If as an American I may take this discussion out of the purely British scene for the moment:

On three occasions back in the last century, I attended performances by Townes Van Zandt, whose music I admired on his best recordings. (His recorded output was uneven.) On each live occasion he appeared drunk or stoned -- in other words, impaired and uninteresting. As a cash-paying audience member I felt insulted, furious, and robbed. The last time it happened, I vowed to see him no more. In fact, I had stopped listening even to his albums in the years before his death. Even now I hear them only rarely.

The moral of the story: If you're a musician who feels the need to get shit-faced, do it at home or among like-minded associates. Your fans deserve a whole lot better. I say that, by the way, as a happy consumer of Eliza Carthy's recordings. After her recent pronouncement, unfortunately, I'd hesitate to pay good money to see her in person.