Real time data is available for system frequency and electricity demand. Demand data can be viewed over three separate time intervals: 60 minutes, 24 hours and the last 8 days. Frequency traces track movements over the last 60 minutes.
Dynamic Demand has a cool “frequency” web-meter operating directly from National Grid data. They also show how past events, such as the silence for London bomb victims, have affected the grid. It would be very interesting to see the effect on the demand if we organized an event like Earth Hour.