(20)For a number of activities related to official controls, the European Committee for Standardisation (CEN) has developed European Standards (EN Standards) appropriate for the purpose of this Regulation. These EN Standards relate in particular to the operation and assessment of testing laboratories and to the operation and accreditation of control bodies. International standards have also been drawn up by the International Organisation for Standardisation (ISO) and the International Union of Pure and Applied Chemistry (IUPAC). These standards might, in certain well defined cases, be appropriate for the purposes of this Regulation, taking into account that performance criteria are laid down in feed and food law in order to ensure flexibility and cost effectiveness.