Lights are off for Landing and take off because it is dark outside. If you have ever been in a lit room then turned the light off you cant see a thing, but after a while your eyes adjust to the dark. If there is an emergency and you need to get outside, your eyes will be adjusted because you will have been in a dark place already.
Your window blinds should be 'UP' so EVERYONE can see outside conditions in case of emergency, and the emegency services can see in if need be.
This should be the case wherever you fly, day or night, an not just in the uk.
Hope that helps
