Section 203 of the U.S. Copyright Act, which is being tested in the courts now by the songwriter for the Village People. For readers who are unfamiliar with this law, the principle is simple – assignments made after 1977 can be terminated after 35 years. This applies to song copyrights (musical works) or to sound recording copyrights. The rules and regulations to make the termination are complex and can be found in Section 203. (Because of their complexity, the advice of an attorney is recommended when seeking to terminate.) Notices of termination must comply in form, content, and manner with requirements in a regulation issued by the Register of Copyrights.
What about British copyright law? Whenever we venture outside U.S. copyright law, we must disclaim that our knowledge is cursory. That said, there's no equivalent to Section 203 in British law. Britain does have a reversionary right that permits the termination of transfers (made by the author), 25 years after the death of the author. So, for example, the heirs of Ian Curtis, the songwriter for Joy Division, who died in 1980, could terminate his assignments and reclaim all his rights in 2005. Section 14 of Canada's copyright act provides a similar rule (though most of the other former British colonies have not adopted the principle).