Triple murderer Erin Patterson suffered a substantial miscarriage of justice during her high-profile trial, her lawyers will argue as an appeal begins.

Patterson’s fight to quash her convictions will start in the Victorian Court of Appeal on Wednesday, close to a year after she was sentenced to life behind bars for murdering her lunch guests.

A jury found the 51-year-old deliberately served beef Wellingtons laced with death cap mushrooms to her former in-laws Don and Gail Patterson, 70, and Gail’s sister Heather Wilkinson, 66.

The three guests died after the July 2023 lunch at Patterson’s Leongatha home, in regional Victoria, while Heather’s husband Ian Wilkinson fell seriously ill from the meal but survived.

Patterson was also convicted of Mr Wilkinson’s attempted murder.

In her application for appeal filed with the court, Patterson’s lawyers argued she suffered a substantial miscarriage of justice during her trial.

The lawyers pointed to the “unfair and oppressive” cross-examination Patterson faced, the contents of the prosecutor’s closing address and the implication to the jury she had a motive to kill.

There was also a “fundamental irregularity” during the deliberations as jurors were sequestered to stay in the same hotel as the police informant and members of the prosecution team, lawyers claim.

Patterson’s lawyers argued that placement fatally undermined the integrity of the jury verdicts and required the quashing of Patterson’s convictions.

Prosecutors are separately appealing Patterson’s sentence, arguing her 33-year non-parole period was manifestly inadequate.

Prosecutors were pushing for a prison sentence of life without parole but Victorian Supreme Court Justice Christopher Beale showed Patterson mercy by allowing her the possibility of leaving prison in her 80s.

The judge reasoned she faced difficult conditions in custody, including being in solitary confinement for at least 22 hours a day.

Patterson’s appeal hearing will start at 10.15am on Wednesday and is set to run for two days.

She is not expected to attend court in person, instead watching on a video link from prison.

-AAP