High Court judges have delayed their decision in a dispute over an all-postal ballot in the port of Hull.
The legal row centres on the all-postal ballot
The High Court has been told how an unknown number of voters received the wrong papers for the Derringham ward in the local elections last May.
The independent candidate John Considine, who lost by seven votes, wants a new election to be held.
Mr Justice Jack has said the court would reserve its judgement "no longer than was necessary."
The urgency of the case was understood, he added, saying a judgement would be given "whilst the matter is still fresh in our minds."
In the days before the poll an unknown number of electors in the Derringham ward received postal ballot packs which contained ballot papers for the Marfleet ward which is on the other side of the city.
Mr Considine's counsel, Helen Mountfield, told the court: "It cannot be said how they would have voted if they had received the correct ballot papers. It cannot be said how many of them ever appreciated the error, or took successful steps to correct it.
"What can be said is that at least 17 electors did not receive the correct ballot papers and were accordingly deprived of their opportunity to vote in the Derringham ward election".