A lot of people reacting here with a "But they're a Charity, so they most be good people" clearly are unfamiliar with the problems of Unpaid Internships in London and the scammy nature of so many UK-based Charities nowadays, especially the kind that's based in London, has junior "Personal Assistant" positions and whose "charitable objective" is the same as their name, an "painfully obvious bad thing", in a part of the "good will market" that's not yet saturated (such as for example the fight against hunger would be) and so broad that them having no measurable impact is normal and which as problem that will never be totally solved - the entire thing reeks of a "business" set up by a Politician or MBA to pay themselves vast fortunes as CxO by preying on the good will of well intentioned people.
I lived for over a decade in London and that whole adverts rings several alarm bells in my mind.