"There's no doubt that the salary offered would normally (in London)be that expected by a junior marketing manager with a couple of years' experience. An experienced marketing director of a charity would expect a salary of six figures."

That's not true. There are charities and there are charities. You can't simply say "a charity" like that, as if "working for a charity" had a fixed salary. I agree that the marketing director of, say, Cancer Research, or similar would expect and get a much larger salary (though not a six-figure one). For the obvious reason that cancer is of much more interest to the general public than folk music.

The junior marketing staff where I work get paid around 18/19K. Someone who has come up from an arts background could feasibly have a good 7 or 8 years experience and still find that salary attractive. In today's job market, with people being laid off left right and centre, I don't think they'll struggle to find someone with a good 10 years' experience to do that job.