Seems to me like Speedyhen and Wordery are using the EU vote to jack up prices. The pound lowering is a knee jerk reaction to something that has had no real effect on anything yet but it's the only reason for omnibuses being an average of £40 now being between £70 and £80.
I ride mountain bike trials and the go to shop in the world is Tarty Bikes which is an English company. They didn't raise their prices, they put out an update saying prices were now cheaper for the international buyers. That seems to me that these shops have made a conscious choice.
I'd accept new stock having a jacked up price as a reality of some guys deciding the pound is worth less regardless of anything actually happening (I watched The Big Short, I know how the world economy works ) but books these shops have had in stock for a while shouldn't suddenly have a price increase.