Title 21 of the Code of Federal Regulations (C.F.R.) Section 175.300 is a U.S. Food and Drug Administration (FDA) regulation governing food-contact "Resinous and polymeric coatings." Since these substances are typically complex and often cross-linked compounds, FDA lists cleared precursor materials in this regulation. This regulation also sets forth end tests that the finished coating must meet. This includes a 0.5 mg/in² (or 50 ppm) overall migration limit of total non-volatiles from the coating in its finished form to food. While companies are free to create their own tests, the testing must yield results that can be equated to those listed in the regulations so that if tested according to the regulation, it can be demonstrated that the coating complies with the regulatory limit. (For more information on this regulation, see the PackagingLaw.com article, What's Under the Coat of Section 175.300?)

You also asked about BS EN 14235. BS refers to British Standards and EN refers to European Standards. However, the correct name is CEN/TS 14235:2002 ("Materials and articles in contact with foodstuffs. Polymeric coatings on metal substrates. Guide to the selection of conditions and test methods for overall migration"), since this is a Technical Specification (TS), not a standard. It was developed by the Technical Committees of the European Committee for Standardization (CEN) as a pre-standard that contains technical requirements in anticipation of eventual future harmonization. It can be transposed at national level in the Member States (eg., in the United Kingdom, it was adopted by the British Standards Institution as DD CEN/TS 14235:2002).

Coatings are not the subject of harmonized legislation in the EU but they must be used in compliance with the Framework Regulation (EC) 1935/2004 and national legislation of Member States, where it exists. Generally, overall migration (OM) tests on metal packaging are conducted according to the protocols that have been established specifically for plastics. The Plastics Regulation (EU) No 10/2011 limits OM to 60 mg/kg for substances in food packaging intended for infants and small children and 10 mg/dm² for substances in other food packaging. The protocols currently in place for testing OM and those in (EU) No 10/2011, which will be implemented over the next several years, specify that 3% acidic acid should be used as a simulant for acidic foods. However, CEN/TS 14235:2002 suggests that 3% acetic acid does not need to be used for OM testing of polymeric coating on metal substrates.

In summary, unlike FDA 175.300, CEN/TS 14235:2002 is a not legally binding and is applied only on a voluntary basis. However, standards and technical specifications can be important in the EU. First, while harmonized rules might exist, the standards or specifications would set out the details of how compliance with these rules could be achieved in practice. Second, appliance of standards or specifications can also confer presumption of safety and/or conformity to products for which EU harmonized requirements and rules do not (yet) exist.