Paul,
Do those street lights use low pressure sodium lamps? From pics I have seen of British fixtures they look like LPS.
LPS is extremely rare here. It has never caught on the way it has on your side of the pond, namely because it has a color rendering index of 0! However, they are far and away the most efficient HID lamps.
High pressure sodium is extremely common for street lamps here, but their color rendering is still a lousy 22.
Mercury vapor, the worst of the HID family, in terms of light output and efficiency, is still in widespread use too.
