SOCIAL SECURITY FOR MIGRANT WORKERS - AFFILIATION TO A SOCIAL SECURITY SCHEME - CONDITIONS - APPLICATION OF NATIONAL LEGISLATION - AFFILIATION OF EITHER SPOUSE TO A SOCIAL SECURITY SCHEME SUBJECT TO AFFILIATION OF THE OTHER SPOUSE TO THE SAME SCHEME - WHETHER PERMISSIBLE ( REGULATION NO 3 OF THE COUNCIL ; REGULATION ( EEC ) NO 1408/71 OF THE COUNCIL )