Former Conservative MP Dean Del Mastro suffered a setback in his long-running legal battles Wednesday after an Ontario judge dismissed his application to have a mistrial declared in his election overspending case.

Del Mastro, a former parliamentary secretary to Prime Minister Stephen Harper, was convicted last fall of violating the Canada Elections Act during the 2008 election. He has since resigned his House of Commons seat.

At what was supposed to be a sentencing hearing last month, court heard that Del Mastro's lawyer had filed an application for a mistrial, arguing Justice Lisa Cameron had erred in her judgment.

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Cameron considered submissions from all sides and opted to turn down Del Mastro's application, a spokeswoman for the Public Prosecution Service of Canada said Wednesday.

"Counsel has been advised that Justice Cameron has dismissed the mistrial application, with oral reasons to follow," Sujata Raisinghani told The Canadian Press.

Del Mastro was found guilty of exceeding spending limits, failing to report a personal contribution of $21,000 to his own campaign and knowingly submitting a falsified document.

He faces a maximum penalty of one year in jail and a $2,000 fine on each of the three convictions.

He is to appear before Cameron in a Lindsay, Ont., court on Thursday, where sentencing arguments are set to take place.

Cameron has decided to allow three out of 10 victim impact statements put forward by the Crown to be submitted as part of those arguments, Raisinghani said.

The statements were contested by Del Mastro's lawyer, Leo Adler, who argued the people making them amounted to a collection of the former MP's political opponents. If the statements were to be allowed, Adler had asked to be able to cross-examine the victims.

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Cameron granted Adler a partial victory on that front by dismissing the bulk of the statements.

"She has admitted three victim impact statements, subject to judicial editing," Raisinghani said. "Cross-examination of the victims is not permitted."

When asked to comment on the developments in the case, Adler said he would be responding to the matter in court on Thursday.

Crown prosecutors had argued Del Mastro's mistrial application was an attempt to appeal the judgment in the case.

Crown lawyer Tom Lemon had told Cameron that Del Mastro received a full and fair trial and argued the former MP "doesn't get a do-over because he doesn't like the result."

But Adler, who was hired by Del Mastro after a judgment was rendered in the case, had countered that the mistrial application was valid.

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His arguments centred on a contract between Del Mastro and a now-defunct data-consulting firm whose voter identification and get-out-the-vote calling services had pushed the former MP over his campaign spending limit.

Adler said Cameron never stated the contract was completed in full, which left the case with "a missing element."

Cameron noted, however, that the prosecution's case was about exceeding election expenses, not about whether a particular contract was completed.