The Returning Officer in an election must not accept any ballot paper that is –

(a) received by the Returning Officer after the close of the ballot; or

(b) contained in an envelope where the voting declaration has not been signed as required under regulation 21 ; or

(c) received from a person who is not (or in the reasonable opinion of the Returning Officer does not appear to be) eligible to vote in the election; or

(d) received from a person who, except as permitted by regulations 15 and 16 , has already voted in the election.