The British Board of Film Classification has been busy.

Last year, the group rerated more than 30 older films to meet contemporary standards. In February, it gave a stricter rating to “Mary Poppins” because of racial slurs. And last week, it began using an updated set of guidelines after surveying thousands of British moviegoers to gauge shifting public attitudes.

Based on that survey, the new guidelines acknowledge that audiences have grown more lenient about depictions of cannabis use but are more concerned about intense violence and, for younger viewers, bad language.

“We follow what people tell us, and we update our standards as societal attitudes change,” said David Austin, the board’s chief executive.

When distributors rerelease movies in theaters, on streaming services or on DVD, they may be required to resubmit the films to the ratings board. Many voluntarily choose to do so, Austin said, in hopes of receiving a lower rating or to ensure that the rating matches the content. What was once considered acceptable onscreen may no longer be.

Under the newest guidelines, the board said, both the 2018 Transformers movie, “Bumblebee,” and the 1963 James Bond classic, “From Russia With Love,” would be rated 12A instead of PG if they were resubmitted for updated ratings.

(The ratings for theatrical releases are U, for universal; PG, for parental guidance; 12A, 15 and 18, for certain age restrictions; and R18, for pornographic content.)

A distributor is legally required to ask for a new rating when it rereleases a movie that was classified before the introduction of the modern ratings in 1982. The B.B.F.C. said that about half of the theatrical releases it rerated in the past two years were mandatory submissions.

“Rocky,” which was released in the United States in 1976 and in Britain the following year, received a 12A rating for its 2020 theatrical rerelease because of moderate violence, mouthed strong language and domestic abuse. “Enter the Dragon,” a 1973 film starring Bruce Lee, went from an outdated X rating to 15 as attitudes evolved regarding the weapons and violence depicted in martial arts movies.

Although older films are regularly reclassified in Britain, similar changes rarely happen in the United States, where studios do not have to submit their films for reclassification, even if the films were rated before 1984, the year that PG-13 was introduced.

The American ratings group, the Classification and Ratings Administration, does not have a systematic process for updating the guidelines for its ratings (G, PG, PG-13, R and NC-17). It provided one example of a film that it rerated: In 2010, a singalong version of “Grease” was rated PG-13, instead of its original PG in 1978.

The group is a division of the Motion Picture Association, a trade organization representing major Hollywood studios. Its board is made up of parents who have school-age children, a CARA spokeswoman said.

CARA conducts regular surveys with American parents to gauge attitudes about violence, nudity and other content in films, and the board uses that feedback when it rates movies, according to an M.P.A. spokesman. The results from the most recent survey, which were released in April 2023, show that parents are most concerned about graphic sexual content, nudity, sexual assault, suicide, use of hard drugs and racial slurs in movies that children might see.

Movie studios in the United States prefer to self-regulate their films, said Kevin Sandler, an associate professor in the film and media studies program at Arizona State University and the author of a book about Hollywood film ratings.

“When there’s some kind of controversy that’s brewing and push comes to shove, they’ll change it,” Sandler said.

Last year, viewers of “The French Connection” on Apple TV+ and Amazon noticed that a scene with a racial slur for Black people had been quietly excised. On Disney’s streaming platform, the company has added warnings about “negative depictions” and “mistreatment of people or cultures” to classic animated films like “Dumbo” and “Peter Pan.”

The British Board of Film Classification, which consists of business leaders, former journalists, a former lawmaker and a social worker, is nongovernmental and a nonprofit, according to its website. But the government does designate the board’s leadership with the power to classify video releases.

Its classifications can have a significant effect on which movies British parents allow their children to see, said Julian Petley, a professor at Brunel University London and one of the principal editors of The Journal of British Cinema and Television.

“They have a massive public consultation process,” Petley said. “They’re not just guessing at what people think or reading off newspapers.”

In recent years, the board reconsidered “Watership Down” (1978), which went from U to PG because of mild violence, bloody images and language, and “The Lord of the Rings: The Fellowship of the Ring” (2001), which changed from PG to 12A for its fantasy violence. “The Empire Strikes Back” (1980), originally rated U, received a PG rating for several violent scenes, including one in which Luke Skywalker’s hand is severed.