51. (1) A ballot paper shall at the time of issue be marked with an official mark (in this Schedule referred to as “the official mark”), which shall be either embossed or perforated so as to be visible on both sides of the paper, and the local returning officer shall provide a sufficient number of marking instruments for this purpose.

(2) The returning officer shall ensure that the official mark is kept secret before the taking of the poll and that an interval of not less than 10 years shall intervene between each use of the same official mark at a European election in the constituency.