There is NO right to light anymore in the UK. New planning laws are changing this. It was in the press a couple of weeks ago. Your neighbours should be the ones to investigate this, not you.
UK
You should be very careful. Rights of light still do exist, and if you do not investigate this you could have a very serious problem. Happy to discuss 0845 519 7703, or visit www.righttolightsurveyors.co.uk
The house next door is worried?
Call a priest. That house needs an exorcism.
Houses do not worry about light.
Answer 1 is quite correct, answer 2 is semi-correct and answer 3 is total rubbish - right to light under UK law is still alive and kicking.
Maybe it's you.
We are building a two storey building and a house next door is worrying about the amount of light, who pays for the survey?