Minister Louis Farrakhan, controversial leader of the Nation of Islam, has been denounced by some as the "minister of rage" and the "black Hitler". Accused of anti-semitism, he has been banned from Britain since 1986. In this Correspondent investigation, Gary Young examines what Farrakhan means to African-Americans, and asks why a leader of Black America is officially unwelcome in this country. Is the problem the messenger or the message?