++++ 1.Social security for migrant workers - Voluntary or optional continued insurance - Option of retroactively paying pension rights subject to affiliation to the national scheme of compulsory insurance - Condition not satisfied by affiliation to the compulsory insurance scheme of another Member State ( Regulation No 1408/71 of the Council, Art . 9 ) 2.Social security for migrant workers - Voluntary or optional continued insurance - National legislation making the right to purchase pension rights subject to affiliation to the national scheme of compulsory insurance - Condition required of nationals - Permissible ( EEC Treaty, Arts 48 and 51 )