I signed settlement under duress: Hird

UPDATED: Suspended Essendon coach James Hird has claimed he was ordered by the club to say he would take "full responsibility" for the supplements saga - and that he only agreed to his suspension following "threats, duress and inducement".

On day one of the Federal Court bid by Essendon to have ASADA's investigation into them declared invalid, the suspended coach and Brownlow medallist was the star witness.

Cross examined by ASADA lawyers, Hird told the Federal Court he disagreed with many decisions the club made about how to handle the doping investigation - but felt he could not voice his dissent publicly.

And the coach also repeated the fiery allegation that former chairman David Evans told him to co-operate with the investigation and tell the truth - apart from details of a conversation from the day before Essendon's press conference, in which then AFL chief Andrew Demetriou alerted the club to doping claims.

"I was asked by the Essendon Football Club not to shirk the issue," Hird said.

"I was told it would be better for the club if we went along this path."

Earlier the club and Hird launched their double-barrelled legal attack on the AFL and ASADA's joint investigation into the club's suspected doping regime, arguing it was unlawful and unjust.

Hird and his wife Tania were intent observers as the Federal Court in Victoria began hearing the bid to have the investigation ruled outside of ASADA's powers, which could lead to the show cause notices to 34 players being ruled invalid.

In opening their case, lawyers for Essendon said that a ruling against them could "destroy their business", while ASADA claim an adverse finding against their investigation would have serious implications on future investigations into drugs in sport.

Neil Young QC for the club described the joint investigation as a "Faustian pact" which trampled over the regulations which framed ASADA's powers.

And Peter Hanks SC, Hird's lead cousel, said the investigation was "infected by jurisdictional error".

"The injustice to the 34 players from this unlawful investigation is a compelling consideration for grant of relief," Mr Hanks said.

He also accused ASADA of agreeing with an AFL request to "tailor" their interim report so the league could use it to impose their own sanctions on Essendon.

Essendon chairman Paul Little, right, and lawyers arrive at the Federal Court ahead of the case looking into the AFL-ASADA Investigation into the alleged use of banned substances at the Essendon Bombers Football Club on August 11. Picture: Scott Barbour/Getty Images

Both Hird and the club claim ASADA unlawfully used the AFL's compulsive powers to gain information they could not have got otherwise - and then gave the information back to the league bosses, against their confidentiality provisions.

David Grace QC, for the players, argued they were placed in an invidious position, after being warned if they didn't cooperate they could face AFL or even criminal sanction.

But Tom Howe QC, lead counsel for ASADA, said the players - as part of their contractual agreement with the AFL - were bound to cooperate with any investigation.

"Both parties (Essendon and Hird) and all the players unambiguously agreed ... to that very sort of of acquisition of information," Mr Howe said.

And ASADA strongly argued the joint investigation was legal and allowed for in law, and the same information could also be "reacquired" with new powers granted by the government.

Documents arrive at the Federal Court ahead of the case looking into the AFL-ASADA Investigation into the alleged use of banned substances at the Essendon Bombers Football Club on August 11, 2014 in Melbourne, Australia. Picture: Scott Barbour/Getty Images

Mr Howe, concluding his openings, described the Essendon management under Hird as "toxic", "abysmal" and seriously derelict - and said the club's argument that their management was not connected to the drugs investigation "defied credulity".

"It was part and parcel of it, and it was the very thing that prompted officers from Essendon to approach ASADA," Mr Howe said.

He also argued that if it was ultimately ruled that ASADA should not have been able to share their findings with the AFL,that would have serious implications for future investigations.

"It would be anomalous and wholly perverse - the phrase nonsense on stilts comes to mind," Mr Howe said.

The hearing is scheduled to run for three days.