Dear gxnml,
178/2002, or General Food Law, is the basic of all food laws. It includes the requirements for traceability, the establishing of the EFSA, Rapid alert system, responsibilities for food operators, risk assessment, protection of consumers and some general issues, like the definition of unsafe and unappropriate food and feed.
852/2004 is part of the hygiene package which also includes 853/2005 (animal products), 854/2004 and 882/2004(control and inspection by authorities) and 2073/2005 (microbiological criteria). 852/2004 states requirements on food hygiene for food operators, the obligation to use
HACCP system, guides for good practices, etc.
Almost all these requirements are also included in BRC/ IFS/ PAS 220/ etc.
you could say that 178/2002 is the start and the hygiene package is the sequal. 852/2004 refers several times to 178/2002.