F3Subject to paragraph (4), if required by the F1applicable NTSN, the procedures for assessing the conformity or suitability for use of an interoperability constituent must be carried out by F4an approved body or, where assessment against an applicable UK specific case is required, a designated body.

The appropriate procedures for assessing the conformity or suitability for use of an interoperability constituent are, subject to paragraph (3), the procedures indicated in the F1applicable NTSN.

Spare parts for subsystems that were placed in service before the applicable F5NTSN came into force are not subject to the procedures referred to in paragraph (2).

Except for cases which fall within regulation 23(2), where an EC declaration of conformity or suitability for use has already been drawn up, an assessment of the conformity or suitability for use against an applicable UK specific case must be carried out by a designated body in accordance with the procedure set out in the NTSN concerning the further assessment of interoperability constituents which hold an EC declaration of conformity or suitability for use.