BBFC (British Board of Film Classification) - U Rating and What Applies

The rating (U), meaning universal for all, means that the film is suitable for all those of 4 years or older. Films under this classification should be set within a positive framework and contain a reassuring counterbalance to any violence, horror or threat.
Discrimination: Behaviour or language deemed to be discriminative is unlikely to be acceptable unless very clearly disapproved of within the feature.
Language: Only very mile bad language that is used infrequently will be acceptable.
Nudity: Nudity must be occasional and not to be seen within a sexual context.
Sex: Sexual behaviour of a mild nature (i.e. kissing) and references to such behaviour is accepted.
Threat: Potentially scary or unsettling sequences should be infrequent, brief and mild with a positive outcome and unlikely to cause anxiety to younger children.
Drugs: Use or reference to illegal drugs must be infrequent and incongruous, or portray a clear anti-drug message and educational purpose suitable for young children. Anti-social or potentially  dangerous behaviour which young children may copy must be clearly disapproved of and no realistic or easily accessible weapons are to be included.
Violence: Violence should be generally very mild. Mild violence will be acceptable if justified by context (i.e. wholly unrealistic, comedic, animated).