"The land was transferred to Waitakere Council free of charge, and then to the Auckland Council in the same way," Mr Carruthers told the Court of Appeal today.
The plaintiffs said the land should have been offered back to them by law in 1982, when an amendment to Section 40 of the Public Works Act was passed.
That law ordered government agencies to offer land back to original owners when it was no longer needed for essential works.
Justice Harrison told the court today it was widely accepted the land in question was "worth more than 60 or 70 million dollars".
Justice Harrison asked various questions about the land's status, if it was an ecological reserve, and sought to clarify if Mr Carruthers' clients would have to apply for a zoning change.
Mr Carruthers said he understood it was open space, and added "if it is a reserve, it is in a category of reserve that can be reversed".
He said local authorities could instigate this possible change.
After today's hearing, Mr Carruthers said his clients were content to have gone to the Court of Appeal after an earlier High Court hearing.
In that hearing, the council raised nine objections.
The first eight were thrown out but the seven plaintiffs lost their claim on one point.
In the High Court decision last year, Justice John Fogarty said the Auckland Harbour Board and Waitemata City Council Empowering Act 1983 ended the board's obligation to offer back the land to them.
Mr Carruthers contended the Court of Appeal took a dim view of that High Court decision.
"The court was plainly not at all impressed with that argument, which means that I expect I'll succeed on that point on appeal. But then there's a cross-appeal on a whole succession of points, but I think the case will probably turn on the exercise of the residual discretion of the court to grant a declaration."
Mr Carruthers said it was yet to be decided what would happen if the Court of Appeal decision was not in his clients' favour.
An option to apply to the Supreme Court was available but the higher court's acceptance of that was not guaranteed.
"It depends on establishing a case of public or commercial importance. Historically, the Supreme Court hasn't allowed cases of this nature under this particular section to go to the Supreme Court."
Speaking on behalf of Auckland Council today, Matt Casey QC said the land in question was a "significant asset" and there was a "very high public interest" in having the Council case heard.
Yesterday, Mr Casey argued the plaintiffs had known for some time the board was not planning to use the land for port purposes.
He said by 1982, the council was not holding the land for public works, but for industrial development.
Justices Harrison, French and Mallon reserved their decision and would issue a written decision later.
"This is a difficult case and it raises many issues that we'll have to grapple with," Justice Harrison said.
