Language: The cussing room floor

Ken Loach is the latest director to complain about censorship, says Tim Walker. The rules on swearing are so arbitrary, it's no wonder he's effing and blinding

Ken Loach's long and illustrious showreel contains vivid scenes of animal cruelty, terrorism and domestic abuse. Yet when the firebrand director was asked by British censors to make cuts to his new film The Angels' Share, it was for the mundane crime of containing too many swear words. To achieve a 15 certificate, Loach claimed at Cannes this week, "We were allowed seven 'cunts'." The quota system for bad language, he said, is "surreal".

The BBFC's guidelines are based on a public consultation conducted every four years, the last of which was in 2009. Language tends to be the least controversial issue for audiences, but the most controversial for film-makers. Loach has wrestled with the delicate sensibilities of the censor before. In 2002, his Palme D'Or-nominated Sweet Sixteen was awarded an 18 certificate for its 20 C-words and 313 F-words, meaning the teenagers portrayed in the film would be unable to see it.

His predicament recalls the row over the certification of Made in Dagenham in 2010. Producer Stephen Woolley was outraged when his film, which told the story of the 1968 women's strike for equal pay at Ford, was given a 15 certificate for its 17 uses of the F-word. He believed younger audiences would benefit from its message of equality and empowerment. "The BBFC surmises that the F-word will deprave or corrupt 13-year-olds," he wrote. "Who are these delicate flowers who have never been in a playground... or heard a rap record?"

In the same year, much to Woolley's chagrin, The King's Speech was awarded a 12A, despite repeated use of the F-word. The BBFC allowed it because it appeared "in a speech-therapy context" in the film. This led to accusations of classism by the censor, which appeared to deem posh "fucks" acceptable, but not working class ones.

Extreme violence, meanwhile, finds its way into 12 certificate films with increasing regularity. This year, the makers of The Hunger Games made cuts to earn a 12A rating, yet the film still features children being brutally killed by other children. The most controversial C-word of recent years was uttered by 11-year-old Chloe Moretz, in the 15-rated Kick Ass (2010); four letters subjected to far more censure than her character's multiple violent murders.

Perhaps it was to avoid such disapproval that 12A blockbuster Avengers Assemble (2012) looked to the past for its single instance of swearing, with a word so long out of service in spoken English that it's actually more shocking to hear: the evil Norse god Loki insults female super-agent Black Widow, calling her a "mewling quim".