Film Certificates;

The film certificates in the UK are decided by the British Board of Film Classification this has been running since 1912, for cinema releases as it falls to councils to decide who should be admitted to a certain film, effectively making them legally-binding. The classifications are as follows: 

15 suitable for those aged 15 or older 
(this may include content involving strong language, strong violence or sex references)

U (Universal) which is classed as suitable for all people all ages 

18 suitable for those aged 18 or older
(this may include content with very strong language, 

sex, racism, bloody violence)

PG (Parental Guidance) which is classed as general viewing but some scenes may be unsuitable for children 

12 which is classed as for those the age of 12 and older but in cinemas children under 12 may enter if joined by an adult
(this may include content involving strong language, sex references and mild violence)