Is there a bike light law?

What if I'm fixed to the bicycle then...
Head light is better then fixed cos you can direct it toward cars to make sure they see you. And I don't want to have to take my back light off every time I lock my bike up

The law is the law. Feel free to break it. Don't complain when you get fined.

I pefer a handlebar light on the road and a bar+helmet light combo for offroad.
I don't tend to need to 'examine' terrain and lines through corners when on the road.
It takes less than a second to unclip my rear light and put it in my pocket. I don't see how this can be considered an excuse. But people will come up with any old crap to justify their actions. meh.