Recently, the UK Secretary of State for the Department of Culture, Media and Sport (DCMS) Andy Burnham did an interview with The Telegraph. During the interview he confirmed that the government was looking into a cinema-style rating system for websites.
As a web developer, hosting provider and internet user, I do not understand how such a scheme would be possible. There are a number of issues that need to be considered before anything like this is implemented in this (or any other) country.