I'm a huge fan of Purdey's gear, I've been lucky enough to shoot some of their guns, though as yet, not to own one

What you have to remember is that Purdey is one of those superb London stores that has been around for ages making luxury goods. As such it can charge pretty much whatever it likes for anything because the type of people who buy things from the store itself wouldn't bat an eyelid at £850 trust me.
As a community we always seem very anti people charging extortionate amounts for things, and I understand why. It's because it represents consumerism and ignorance and extortion yada yada. But from a more simplistic point of view, if you ran a shop that could charge excessive amounts for its goods and gets away with it...wouldn't you? Can we really ever blame people for making money? We can scoff at how expensive stuff is and say it's ridiculous, which of course it is - that sharp is worth nowhere near that and I'd never buy it when I could buy something superior for less....
But someone will