He didn't break the bank. The bank broke itself.
> What kept the pound from plummeting in value was the British government’s guarantee that it would keep the value propped up, and the market believed that it would. As long as everyone believed that England would stay indefinitely committed to buying pounds for around 2.95 Deutschemarks, the status quo was maintained.
If you build a house on rotten stilts, and some neighborhood kid comes and kicks one of them, it's not the kid's fault when the house collapses.