Nah, the obvious answer is the public, people on sites like this and others, it's The Big Society isn't it, and we're the ones that seem to care. At the bottom it could say, discretely, Provided by the Friends of Silbury...
The good thing about that is we could maybe have a bit of a say in the design, and be allowed to source them, probably from China, for a very small fraction of what EH pays....