Institutions for occupational retirement provision which also operate compulsory employment-related pension schemes which are considered to be social-security schemes covered by Regulations (EEC) No 1408/71 and (EEC) No 574/72 shall be covered by this Directive in respect of their non-compulsory occupational retirement provision business. In that case, the liabilities and the corresponding assets shall be ring-fenced and it shall not be possible to transfer them to the compulsory pension schemes which are considered as social-security schemes or vice versa.