1. (a) Whether a national law which, by way of exception to the general provisions concerning the recovery of undue payments, provides that certain charges (including, in particular, health inspection charges) unduly levied contrary to certain provisions of Community law, inasmuch as they are charges having an effect equivalent to customs duties, may be repaid only if it is proved that the charges have not been passed on to other persons, but does not subject the repayment of any other tax, charge or duty wrongly levied to the same condition, is to be regarded as discriminatory, contrary to the principles of Community law; and whether it is significant that the charges covered by the abovementioned provision have been wrongly levied solely inasmuch as their collection conflicts with a rule of Community law; (b) Whether the requirement of negative documentary proof, the sole condition to which the aforesaid national law subjects the repayment of charges unduly levied, renders ‘the exercise of rights which national courts are under a duty to protect virtually impossible’. 2. Would the Court state whether, as from 1 July 1980, the date of the entry into force of Council Regulation (EEC) No 1430/79 of 2 July 1979 on the repayment or remission of import or export duties, which, according to the terms of Article 1 (2), applies to customs duties and charges having equivalent effect, a Community system was introduced for the first time governing the repayment of charges unduly levied, without however providing for any exception where the charges are passed on to other persons; and whether that system takes precedence over any previous or subsequent national law.