First came the split; then the restraining orders.

Now, the lawyers attempting to thrash out a child-custody agreement between Mel Gibson and his estranged former girlfriend Oksana Grigorieva find themselves at the centre of a rapidly snowballing race-relations scandal.

Transcripts of secretly recorded tapes, allegedly made during domestic disputes between Gibson and Grigorieva, were leaked to the public this weekend, apparently chronicling several violence-threatening, sexist, and casually racist tirades the Hollywood actor launched against the mother of his nine-month-old daughter.

In one, Gibson, 54, allegedly called his partner a "bitch" and a "whore", before warning: "I am going to come and burn the f***ing house down. But you will blow me first." He apparently describes her as a "psycho c**t" and a "f***ing fake".

But it was an outburst which featured a racial epithet that has inspired the most controversy. "You look like a f***ing pig in heat," he apparently told Grigoerieva, 40. "If you get raped by a pack of niggers, it will be your fault."

The comments, condemned by race relations groups from the NAACP to the Anti-Defamamation League, to Jesse Jackson, who said Gibson "needs help", were made public by the show-business website Radaronline. It said Grigorieva also has abusive emails from the star yet to be released.

Lawyers for the two parties met in court in Los Angeles last week. Copies of the tapes, made this year, are already with the judge.

Both sides are arguing over how evidence in what is supposed to be a sealed child-custody case made it into the public domain. But of greater concern to Gibson, in the long run at least, will be the effect they have on his career.

The actor, who is recently divorced from his longstanding wife Robyn, belongs to a conservative Catholic sect. He sat at Hollywood's top table for more than a decade, but has appeared in only one studio film since 2006, when he made anti-Semitic comments at police officers who arrested him for drink-driving. "F***ing Jews," he told a Jewish policeman. "The Jews are responsible for all the wars in the world." Later, he called a female officer "sugar tits".