For our film, the chosen certificate is 12A. These are the elements a 12A film can contain and the website I got the information from.
The ‘12A’ category exists only for cinema films. No one younger than 12 may see a ‘12A’ film in a cinema unless accompanied by an adult, and films classified ‘12A’ are not recommended for a child below 12. An adult may take a younger child if, in their judgement, the film is suitable for that particular child. In such circumstances, responsibility for allowing a child under 12 to view lies with the accompanying adult.