INDEPENDENT Senator Nick Xenophon wants an urgent investigation into a string of mysterious election date bets that were made on the same morning Prime Minister Julia Gillard made the shock announcement.
Online bookmaker Sportsbet confirmed it suspended election date betting on Wednesday morning after it took 10 bets in the hours before Ms Gillard revealed Australians would be heading to the polls on September 14.
Senator Xenophon wrote to Special Minister of State Gary Gray on Tuesday expressing his concerns about the betting plunge.
"Given the announcement of an election date came as a surprise to most, there may be a link between the placing of the bets and those who had inside knowledge of the Prime Minister's plan to announce the election date," Senator Xenophon wrote in the letter.
"While there is no evidence that ministerial staff were involved in placing bets, I believe this matter warrants urgent investigation to exclude that possibility."
Mr Gray called on Senator Xenophon to substantiate his claims.
He said his office had made attempts to contact Sportsbet, but would not be drawn on whether a formal investigation would be launched.
"We should be clear - no one else is claiming there was anything untoward, including Sportsbet," Mr Gray said.
"We are the only side of politics that has a code of conduct for our staff, which makes it clear staff must not use their position to gain a benefit or advantage for themselves or any other person."
Sportsbet had gone to ground by Tuesday afternoon, informing APN Newsdesk it had taken a decision not to comment further.
Earlier in the day, Sportsbet spokesman Hadyn Lane told ABC radio the bets, some of which were in the hundreds of dollars, raised alarm bells because they were made in such quick succession and came after weeks of inactivity on election date betting.
"We obviously weren't aware of any inside information, but the fact that we took bet after bet and again, there weren't tens or hundreds of these bets, but they were in a succession," Mr Lane said.
"So the prudent thing for us to do was to suspend the market until we could get a better gauge of what was going on, hear of anything.
"As it turned out, there was an announcement shortly afterwards."
He said all successful bets would be paid.
Just last week Senator Xenophon and fellow anti-gambling campaigner, Tasmanian independent Andrew Wilkie, called for a ban on election betting after Sportsbet posted markets for all 150 federal electorates.
"Last week we spoke about the dangers inherent in allowing gambling to do with elections," Mr Wilkie told reporters in Canberra.
"Here we are less than one week later and the evidence is in.
"There is a very strong prima facie case that a person or persons were aware of the election date ... (and) laid money in an attempt to win.
"This illustrates the point we were making last week. Not only is it improper to be gambling on an election outcome or the timing of an election, it is open to rorting."
Respected Liberal Senator Arthur Sinodinos said last week's betting splurge might warrant closer examination.
"If there was a plunge just before the Prime Minister made the announcement I think that should be investigated on its own merits," Senator Sinodinos said.
Update your news preferences and get the latest news delivered to your inbox.