Will Smith's thriller I Am Legend received a PG-13 rating in the US
British film censors are toughening their stance on horror and violence in movies, taking a stricter line than their American counterparts.
Requests for 12A ratings for a number of Hollywood films were rejected by the British Board of Film Classification (BBFC), the body's annual report said.
Films like Cloverfield, I Am Legend and Disturbia got a PG-13 rating in the US, allowing access to children of any age.
In the UK, however, the films received the more restrictive 15 certificate.
The BBFC said the ratings showed an "increasing divergence" from the US system, regulated by the Motion Picture Association of America (MPAA).
"While the MPAA takes a strict line on issues relating to nudity and sex, the BBFC is significantly more restrictive on violence and horror," BBFC director David Cooke said.
The distributors of Cloverfield, I Am Legend and Disturbia had been "very keen" for the films to receive a 12A classification, according to Mr Cooke.
That rating means the film is suitable for viewers aged 12 and over. Children under 12 may also see 12A films if they are accompanied by an adult.
Thriller Disturbia starred Indiana Jones actor Shia LaBeouf (left)
But the BBFC felt the films in question should be rated 15 for their "extended periods of intense violent threat and moments of horror".
Films rated 15 cannot be seen in a cinema by anyone under that age.
In the US, PG-13 means anybody can get into the film but parents are warned that some scenes that may be inappropriate for those under 13.
"The board's view was that, based on the extensive public consultation exercises, the films went beyond what most members of the UK public would consider appropriate for children younger than 15," Mr Cooke said.
These were not the only cases, he added. "Around 10% of films each year which come in with a particular category request end up with a higher one than asked for."
The BBFC's current guidelines, published in 2005, were drafted following consultation with more than 11,000 people in the UK.
This year, the body will begin a new programme of consultation in preparation for its next set of guidelines, to be published in 2009.
The BBFC has pledged to consider a number of issues, among them the treatment of such issues as racism and homophobia and the importance of "psychological impact".
"BBFC decisions reflect UK public attitudes," said Mr Cooke, who has been BBFC director since 2004. "Notions of harm and appropriateness remain culturally dependent.
"That is why all past attempts to develop a pan-European film classification system have fallen at the first hurdle."