Lawyers for Ian Bailey have told the Court of Appeal that the High Court unfairly disparaged his primary witness by giving her a dramatic warning about the consequences of perjury in front of the jury.
Mr Bailey is appealing against the jury's decision to reject his claim of a garda conspiracy to link him to the murder of Sophie Toscan du Plantier.
He has submitted 17 grounds of appeal, many of which relate to rulings by the trial judge during the five month long case.
Mr Bailey sued An Garda Síochána and the State for damages.
He claimed he was wrongly arrested on suspicion of the murder of Ms Toscan du Plantier, at her holiday home in Schull in west Cork in 1996.
He claimed some gardai had conspired to frame him for the killing.
On day 62 of the action, the trial judge, John Hedigan, struck out many of Mr Bailey's claims, ruling that they were not made within the time limit required by law.
A claim that certain gardaí were involved in a conspiracy against him in relation to witness Marie Farrell was allowed to go to the jury.
But the jurors found against Mr Bailey after almost two hours of deliberation.
Mr Bailey was ordered to pay the multimillion euro legal costs associated with the case.
A stay has been put on the costs order pending the outcome of this appeal.
Mr Bailey has always denied being involved in the murder of Ms Toscan du Plantier, whose body was found near her home on 23 December 1996.
In their submissions to the court, Mr Bailey's lawyers argued that the High Court judge should have discharged the jury after he "unfairly disparaged" one of Mr Bailey's primary witnesses.
Ms Farrell had given a statement to gardaí identifying Mr Bailey as the man she had seen on Kealfadda bridge in Schull in the early hours of 23 December 1996, contradicting Mr Bailey's claim that he had been at home at the time.
She later claimed she had been coerced into making this statement by gardaí.
After she finished in the witness box, on day 21 of the trial, before the jury left, Mr Justice Hedigan told her to give careful consideration to the manner in which she was giving evidence and to bear in mind that there were very severe penalties for people who commit perjury.
Mr Bailey's lawyers said that giving this dramatic warning in the presence of the jury amounted to a wholly unjustified, unnecessary attack on Mr Bailey's case.
They said the ability of the jury to fairly assess her evidence was irreparably and unlawfully damaged.
They said the prejudice caused by this was magnified when the entire case came to rest entirely on Ms Farrell's credibility, due to rulings made by Mr Justice Hedigan.
Senior Counsel Tom Creed said allowing only the narrow part of Mr Bailey's conspiracy claim, relating to Ms Farrell, to go to the jury was "doomed to fail" as she was such an unreliable witness.
Mr Bailey's lawyers argued that the judge's ruling withdrawing most of the case from the jury was too narrow.
They said Mr Bailey's allegations of a conspiracy went beyond the gardaí named in Mr Justice Hedigan's ruling.
They said there was ample evidence of conspiracy, which should not have been ruled out by the judge's decision that most of Mr Bailey's case was outside the legal time limits, but which was not put to the jury.
They told the court that allegations that gardaí threatened to frame Ms Farrell's husband if she did not give evidence in a 2003 libel action taken by Mr Bailey as well as actions by gardaí in ensuring that the investigation file was sent to France during the first attempt to extradite Mr Bailey, formed part of his conspiracy claim and should have been put to the jury.
In their submissions, Mr Bailey's lawyers also told the Appeal court that the judge's decision to curtail the evidence of former directors of public prosecutions Eamon Barnes and James Hamilton and solicitor Robert Sheehan was wrong and also rendered the jury's verdict unsafe.
They also argued that the trial judge did not rule on a claim by them that Mr Bailey's constitutional rights had been breached.
They claim the trial judge's rulings taken together rendered the trial of Mr Bailey's action unfair.
They want the jury's verdict to be quashed.
The State will reply to Mr Bailey's submissions tomorrow.
Before the appeal opened, lawyers for Mr Bailey said they had only just received a further sworn document outlining further recordings of phone calls at Bandon Garda Station, unearthed by the Fennelly Commission, which was examining the issue of the recordings of calls at garda stations.
The court heard that following a recent front page story in the Sunday Times newspaper, lawyers for Mr Bailey contacted the State to say they had been contacted by the Fennelly Commission to tell them about 15 tapes of phone calls at Bandon Garda Station.
Lawyers for the State said they did not think this had any relevance to the appeal.
The court said it would be reluctant to allow any new ground of appeal to be introduced at this stage but Mr Bailey could introduce a further ground at a later stage, if he wished to.
The French authorities have issued another European Arrest Warrant, in an attempt to have Mr Bailey extradited to stand trial for voluntary homicide.
An application to have that warrant endorsed will be heard by the High Court on Thursday.
Mr Bailey is expected to challenge the attempt to extradite him.
