What a fantastic idea! Reykjavik is turning all its street lights out on Thursday evening at 10pm for half an hour, and encouraging homes to as well. Then on national radio, astronomers will talk people through the night sky.
Last week, when I was trying to take photos of the night sky, I was enormously aware that I had to take advantage whilst I was outside the city. Even on the very edge of London suburbia is completely hopeless.
Sadly I suspect that a similar initiative in London would lead to concerns about car accidents and massed looting or something. Maybe in a smaller town it could work?