Cloverfield was first seen by BBFC examiners in an unfinished state, for advice as to its likely classification category. An advice screening is a facility offered by the BBFC to distributors. The film was rated PG-13 in America, and the distributor was keen to see the film passed at 12A; however, the verdict at this stage was that extended strong threat merited a 15. A further screening for advice took place after some re-editing by the distributor, but in spite of attempts by the distributor to get closer to a 12A, the pessimistic tone and peristent strong menace resulted in a further recommendation for 15.

The device of 'found footage' is used to relay the tale of Manhattan suddenly invaded by a monster that ravages New York, as the inhabitants are attacked by creeper monsters that bite and kill. The use of the hand-held camera plunges the audience right in the middle of a city in chaos and provides a sense of immediacy that adds to the terror, from which there is little relief.

The 'Earth under threat' scenario (or more usually the USA under threat) is familiar to film audiences. The War Of The WorldsKing KongIndependence Day and Godzilla all offer variations on the theme.  Where classification is concerned, attention must be given not only to the individual scenes of violence or horror, but also to the level and persistence of threat, whether that threat is leavened by humour, and also to the outcome of the narrative.

BBFC Guidelines at 12A  state that 'Mature themes are acceptable, but their treatment must be suitable for young teenagers'. Although Cloverfield is a science fiction fantasy, featuring monsters like those in the 12A rated films listed above, there is a difference in tone that accounts for the higher category. The unremittingly dark tone and ceaseless threat to humans, coupled with a pessimistic conclusion, drive the classification up to a 15. It shares its downbeat conclusion and strong, cumulative sense of menace and horror with I am Legend, also classified at 15 (and also rated at PG-13 in the USA).

At 12A the BBFC Guidelines on violence permit 'no emphasis on injuries or blood'. Cloverfield contains sight of a man’s open chest cavity as he is carried on a stretcher, and a woman with blood leaking from her eyes before she is shot by soldiers. This level of detail was felt to be more appropriate at 15, as was the nature of the horror, which offers the 'strong threat and menace consistent with Guidelines for 15.

In spite of the distributor’s request for a 12A, the film was passed 15 with the BBFCinsight 'Contains strong threat and moderate horror'.

Cloverfield was selected for National Schools Film Week 2008.