RE:GBP strengtheningThey should buy puts on the GBP and sell calls with the same premium. Would cost them nothing and it would take away the doomsday scenario where their cash flow drops dramatically in USD terms. They do that and confidence in their guidance would return.
..or just roll the dice that the UK says stay. But I can't believe that Mark would wager 600 mill of his equity on a 50/50 vote