Fox joined the Revolutionary Communist Party (RCP) as a student at the University of Warwick. For the next twenty years, she was one of the RCP's core activists and organisers. She became co-publisher of its magazine "Living Marxism", which closed in 2000 after the courts found it had falsely accused Independent Television News (ITN) of faking evidence of the Bosnian genocide. In 2018, Fox refused to apologise for suggesting that evidence of the genocide was faked.