Mr Dreyfus, who is a QC, as well as the parliamentary secretary for climate change, told reporters in Canberra on Wednesday that the case was ''an attack designed to change the balance in the House of Representatives''.

This morning, the Federal Court threw out the sexual harassment case brought against former parliamentary speaker Mr Slipper by his ex-staffer James Ashby.

In a scathing judgment handed down on Wednesday, Justice Steve Rares found that the case was an "abuse of process" which had been carried out for the "purpose of causing significant public, reputational and political damage to Mr Slipper". He dismissed the claim and ordered Mr Ashby to pay his former boss's legal costs.

In the wake of the allegations and court case, Mr Slipper stepped down and then resigned from his role as parliamentary speaker, forcing Labor to appoint one of its own - Anna Burke - to the speaker's chair.

This meant the government lost a crucial buffer vote in the hung parliament.

Today, Mr Dreyfus called on Opposition Leader Tony Abbott to give a full account of his knowledge of the affair.

Labor has previously suggested that Mr Abbott had prior knowledge of Mr Ashby's court action against his former employer.

''I had no specific knowledge of this until I read the newspapers on Saturday morning [when the story broke].

And to the best of my knowledge, no-one in the Coalition had specific knowledge of this until they read the newspapers,'' Mr Abbott told 7.30 in April.

On Wednesday, Mr Dreyfus said that Mr Abbott had ''just about admitted knowing about it.''

Mr Dreyfus also said that the Coalition's candidate in Mr Slipper's seat of Fisher, Mal Brough, was ''up to his neck in this conspiracy''.

Mr Brough has previously urged Mr Slipper to quit parliament over lewd text messages he sent to Mr Ashby - that were published in the course of the court action. The National Times has reported that Mr Brough had extensive contact with Mr Ashby before he made the original complaint. Mr Brough - a former Howard government minister -  has denied there was any conspiracy against Mr Slipper.

Mr Dreyfus said that Mr Brough should be disendorsed as the Coalition's candidate for Fisher. ''[His] position is untenable.''

A spokesman for Attorney-General Nicola Roxon said earlier on Wednesday it had clearly been found that Mr Ashby had abused the process of the court and that the Coalition now had serious questions to answer.

"The Commonwealth welcomes the court's decision," the spokesman said in a statement.

"This shows how dangerously wrong and misleading [Shadow Attorney-General] Senator [George] Brandis can be in prejudging court matters. The Coalition will have some serious questions to answer about their own conduct."
Senator Brandis had previously accused Ms Roxon of securing a "political fix" for the Slipper and Ashby matter.

In October, Mr Ashby settled his case with the federal government for a sum of $50,000 and a commitment from the government to introduce training for all MPs and senators regarding sexual harassment. He still had the civil case against Mr Slipper.

In a Senate Estimates hearing in October, Mr Brandis also said there was "no way in the world" that any court would summarily determine the proceedings (ie, make judgment without full trial).

"I would not have advised a client of mine in a million years that they had any chance of success at all of getting summary judgment on this material," Senator Brandis said.
In a statement  on Wednesday, Senator Brandis said the opposition was carefully studying the reasons given by Justice Rares this morning.

"The Attorney-General has once again behaved inappropriately, and once again shown a misunderstanding of her appropriate constitutional role, in commenting on the case when it remains before the court pending the appeal," he said.

"The Attorney-General has also yet to explain why the Commonwealth settled its side of the proceeding in breach of the Commonwealth's own guidelines."

Senator Brandis noted that Mr Ashby "has already announced he will appeal the decision."
Fairfax has contacted Mr Brough for comment.

With Paul Bibby, Stephanie Gardiner