Mick Keelty has told the Australian Electoral Commission that the missing 1370 votes from the botched WA Senate count are unlikely to be found.
The former Federal Police chief's advice has prompted the AEC to ask the High Court to rule on the WA poll by March 18 at the latest to allow writs for an election to be issued three days later.
Given there must be a minimum 33 days between the issue of the writs and election day, the latest a repeat Senate election could be held is April 26.
Mr Keelty's report into the WA Senate count was received by the AEC on Monday and while it has not been released publicly, some of his key findings feature in documents lodged with the High Court on Tuesday by the AEC's lawyers.
"The inquiry undertaken by Mr Mick Keelty has not identified that the 1370 ballot papers have been found or are likely to be found," the Commonwealth Solicitor-General told the High Court.
"In the unlikely event that the 1370 missing ballot papers were now to be found, they would need to be found in a state where their integrity could be assured. After the extensive searches of the (AEC), Mr Keelty's inquiry and the time that has now passed since the missing papers disappeared, that seems most improbable."
Significantly, the AEC contends in its submission that all seven High Court justices should preside in judgment on the WA Senate debacle because of the "grave nature" of declaring an election entirely void.
The AEC identifies an exquisite dilemma in its submission, noting that the election of the first four senators - three Liberals and one from the Labor Party - was proper and "cannot be impugned".
"The problem is that, even if an election could be partially voided . . . a supplementary election could not reasonably be held for only two vacant Senate places," the AEC said.
The fifth and sixth Senate spots were first awarded to Palmer United Party's Dio Wang and Labor's Louise Pratt but on a re-count they went to the Sports Party's Wayne Dropulich and Scott Ludlum of the Greens.
Clive Palmer's petition to the High Court, lodged on Monday, calls for the first result to stand or the poll declared absolutely void.