Former minister Phil Woolas today launched his High Court bid to overturn a decision stripping him of his Commons seat, saying that freedom of speech at elections was at stake.
As Mr Woolas arrived at the Royal Courts of Justice in London for the unprecedented case, he told reporters he was "hopeful" that he could clear his name.
A specially convened election court declared void the General Election result in Oldham East and Saddleworth.
It removed Mr Woolas as the MP and banned him from standing for election for three years after finding him guilty of deliberately lying about a rival, Liberal Democrat Elwyn Watkins.
Today Mr Woolas's legal team asked three senior judges to rule that the election court misdirected itself in law and made a flawed decision.
As it is the first claim of its kind, Lord Justice Thomas, Mr Justice Tugendhat and Mrs Justice Nicola Davies have also to decide in a two-day hearing whether they have power to hear his fast-tracked application for judicial review.
The legal challenge has been brought on for hearing as a matter of urgency to ensure the seat does not go too long without an MP.
Labour - which immediately suspended Mr Woolas from the party - said it would delay calling a fresh election pending the legal fight.
Mr Woolas is being accused by lawyers for political opponent Mr Watkins of employing a strategy to get elected "of the basest kind".
He was found guilty of illegal practices under election law over comments made in his campaign material that Mr Watkins tried to "woo" the votes of Muslims who advocated violence and that he had refused to condemn extremists who advocated violence against the Labour ex-minister.
The election court judges ruled that, although made in the context of an election campaign, the comments clearly amounted to attacks on his opponent's "personal character or conduct" and Mr Woolas, who beat Mr Watkins by just 103 votes in a bitter campaign, had "no reasonable grounds for believing them to be true and did not believe them to be true".
In his submissions to the High Court today, Gavin Millar QC, argued the election court had misdirected itself on the true meaning and effect of the words "personal character or conduct".
As a result it had wrongly held that Mr Woolas's statements, which were about the "political conduct" of his opponent, were also statements about his personal character or conduct.
Mr Millar contended the election court's interpretation of provisions of the 1983 Representation of the People Act was inconsistent with free speech principles and violated Mr Woolas's right to freedom of expression under Article 10 of the European Convention on Human Rights.
Mr Millar argued: "It gives insufficient protection, in particular, to his freedom to attack his opponent in relation to his campaigning and his attempts to win the support of voters at the election."
Helen Mountfield QC, appearing for Mr Watkins, is submitting that the strategy employed by Mr Woolas "was of the basest kind".
She states in a written argument before the judges that Oldham East and Saddleworth was a constituency "in which the divide between Muslim and non-Muslim had seen riots in 2001 and deep religious divisions since then.
"It is no part of the law to protect freedom of expression where that freedom is abused to make one section of the community angry about, and fearful of, another on the basis of falsehoods."
Defending the decision of the election court, Ms Mountfield said it was "conspicuously cautious in its analysis of the facts of this case and its application of the law to those facts".
It was not only entitled but "undoubtedly right" when it made its decision.
Many Labour MPs have rallied round Mr Woolas and contributed to a fighting fund amid open revolt over the leadership's decision to "hang him out to dry".
Mr Woolas said he was "humbled" and "blown away" by the support he had received.
Constituents, MPs and party members raised more than £30,000 in 48 hours, with donations ranging from £5 to £1,000.
Deputy leader Harriet Harman came under fire from colleagues for cutting the former immigration minister adrift and signalling there was no way back for him.
She said after the election court hearing that Mr Woolas had no future as a Labour MP even if he succeeded in overturning the ruling because lies had "no place" in the party's campaigning.
But Labour MPs said it was unfair to write him off while he was still in the process of appealing against the ruling - airing their criticisms at a party meeting and in the media.
Liberal Democrat deputy leader Simon Hughes said: "Labour's leaders had spoken but since then many Labour MPs have come out in support of Phil Woolas both on and off the record.
"The judgment of the court was clear: Phil Woolas made statements which were not about Liberal Democrat politics but personal attacks on our candidate's character and conduct which he had no reasonable grounds for believing were true and did not believe were true.
"Residents in Oldham East and Saddleworth and across the country will not understand why the Labour Party won't say clearly, with one voice, that there is no place in British politics for this kind of behaviour."
The hearing continues tomorrow.