They have not increased the cost, they have rationally responded to the change in exchange rates. It costs pretty much exactly the same.* It's just that the Pound is worth less. England voted for Brexit, fully knowing that there would be fall-out. Just be glad you still live in one of the greatest financial capitols in the world, and that Brexit hasn't caused all that much pain (yet, at least).
Imagine what a Mac Pro would cost in Zimbabwe or post WW-I Germany. You almost couldn't count all the zeros! Bring local-denominated cash to a store and they would laugh. "Toss it in the furnace - money costs less than firewood!," they might say.
(*Of course, the fact that they haven't decreased the cost over these many years, nor upgraded any components, is the real shame and tragedy.)