TRANSPORT - COMMON POLICY - SOCIAL PROVISIONS - REGULATION NO 543/69 OF THE COUNCIL - MATERIAL SCOPE - VEHICLES OF PUBLIC AUTHORITIES - EXCLUSION - VEHICLES OF A PRIVATE UNDERTAKING USED TO PERFORM A PUBLIC SERVICE - INCLUSION ( REGULATION NO 543/69 OF THE COUNCIL , ART . 4 ( 4 ), AS AMENDED BY REGULATION NO 2827/77 )