Gully told InDaily that around 60 votes submitted to the December by-election appeared to have been completed by a person other than the voter named on the ballot paper.

Some votes, he said, appeared to be cast by a person or body corporate that had already voted.

He said he would send the suspect ballot papers to the Crown Solicitor’s office for investigation, and that some of the allegations related to the by-election, including claims of ballot paper theft, may become “police matters”.

Gully said that he would have already sent the ballot papers under question for investigation, however they are being retained because unsuccessful candidate Kelly Henderson has launched legal action in the Court of Disputed Returns, claiming the election was invalid.

He said the ballot papers would stay with the Electoral Commission until the case was over – and be given to the court if required.

However, he intended to forward the ballot papers to investigators regardless of the outcome of the case.

Henderson’s petition outlining her case to the court, seen by InDaily, says that at least 62 votes in the supplementary election had been identified by the Electoral Commission as “potentially fraudulent” and that the matter was being investigated by SA Police.

“It is probable that the election was permeated by fraud, to a significant extent, rendering the result unsafe,” Henderson claims in the document.

“Person or persons unknown unlawfully accessed voting papers from mailboxes.

“Person or persons unknown fraudulently purported to vote for the entitled voter.

“This included 62 instances of potentially fraudulent votes… identified by the Returning Officer before or during the count.”

Henderson’s petition says that it is unlikely that all instances of fraud were detected by the commission, because “the detected instances relate in part to where the effected voter requested a replacement vote”.

The Adelaide City Council responded in its reply to the petition that the allegations were “neither within the knowledge or information of council, nor are they sufficiently specific, so as to enable council to be in a position to agree or disagree with these facts at the time of reply”.

The voter fraud allegations are just one in a series of serious allegations contained within Henderson’s petition, including that “express warnings” had been sent to “certain candidates” regarding claims they “handled voting papers of electors”.

The petition also claims several city residents who were eligible to vote in the election did not receive voting papers, that the council interfered with the election by removing Henderson’s electoral posters from Victoria Square and that votes were collected at the council’s customer centre in ballot boxes should have been collected by post.

However, the council’s response says that it carried out its duties in accordance with the Elections Act, and that ballot boxes in the customer centre were protected by CCTV cameras and locked up at night.

Councillor Sandy Verschoor, who won the by-election, is not named in any of the documents seen by InDaily in relation to any alleged wrongdoing.

The allegations in the petition have not yet been considered by the Court of Disputed returns and no findings have been made. A preliminary hearing in the case will begin this afternoon.

Henderson was one of 13 candidates who stood for the by-election, and placed eighth. She also ran unsuccessfully for Lord Mayor in 2014.