Exchange rate oddity

At 18:30 today the Sterling/Dollar rate jumped from 1.465 to 1.52, why? Which major markets are open this early today?


UPDATE:
And then at 22:00 the rate dropped back to 1.475. What is going on?

Tokyo opens soon and I see that two Pan European markets, FTSEurofirst and DJ Eurostoxx 50, are open... how, where, why?