Films in which actors black up such as Laurence Olivier in Othello should carry a ratings warning, says the official censor.

Prospective audiences will be able to check whether there are “actors in make-up portraying ethnic minorities” in films after research showed the public are tolerant about such theatrical devices but want to be alerted in advance.

The British Board of Film Classification (BBFC) also announced that it will effectively bar the “n-word” from young children’s films rated PG or U for fear they could copy the language.

Its use in PG and U films will only be allowed where there is a “very clear and strong” educational value such as documentaries targeted at young people.

The moves follow research by the BBFC into the public’s attitude towards racism in films and how they should be rated and classified.

Blackface where actors use make-up to portray black characters has been a longstanding theatrical tradition but declined in popularity in the wake of the civil rights movement of the 1950s and 1960s where it was seen as offensive.

It was common in pre war films with stars who used blackface including Al Jolson, Bing Crosby, Fred Astaire, Buster Keaton, Joan Crawford, Doris Day, Betty Grable, Laurel and Hardy, Mickey Rooney, Shirley Temple and Judy Garland.

It has, however, still featured in later films such as Trading Places, where Dan Akroyd dons a dreadlock wig and Jamaican accent, and Robert Downey’s 2008 film Tropic Thunder where his character Kirk Lazarus appears with a blacked-up face.