Fresh evidence published on parliament’s website overnight also argues it is the responsibility of Premier Steven Marshall to ensure ministerial conflict of interest standards are adhered to, and “if the procedures were not followed, the Premier should explain why”.

Marshall yesterday indicated he would refuse an invitation to address the inquiry, but expected questions on the issues raised when parliament sits next week.

The Labor-led committee heard yesterday from former Planning Commission chair Michael Lennon and current Infrastructure and Transport boss Tony Braxton-Smith, both of whom declared that the question of whether Chapman should have recused herself from the decision to veto a $40 million port proposal on her native Kangaroo Island, where she owns property, was for her alone to decide.

“There’s no doubt that she had the right to make that determination for herself,” Lennon told parliament, while Braxton-Smith said: “I consider that entirely a matter for her.”

“In these circumstances the responsibility ultimately rests with the person [affected], either alone or on advice received from relevant parties,” he said.

Chapman herself told the committee last week she had twice considered whether she had a conflict of interest relating to the port proposal, “and was satisfied that I didn’t”.

But a predecessor as Attorney-General, former Corcoran and Bannon-era Labor frontbencher Chris Sumner, has made his own unsolicited submission to the inquiry, in which he insists the “law is clear that the question of whether there is a conflict of interest is not to be determined by the subjective views of the decision-maker”.

“The decision-maker must consider what the reasonable person would think – this is what the committee must now assess,” Sumner writes.

“There is then the further question of whether there is actual bias or conflict because of the actions of the decision-maker in expressing a view about the project or perhaps because there may be some financial consequences that flow from it.”

The committee has heard evidence that in 2017, as an Opposition MP with no portfolio oversight for the project, Chapman expressed a view to the port’s proponents that they had “picked the wrong location” at Smith Bay, urging them to consider alternatives.

Chapman has also conceded that property she owns on the island, which is used as an AirBNB, sits adjacent a forest contracted to Kangaroo Island Plantation Timbers for logging, with proposed haulage routes coming within “one to two kilometres” of her land – but insisted that “that was of no detriment to me”.

Sumner suggests several ways in which a perceived or actual conflict may be present, noting “if it is clear that a decision-maker has been actively involved in opposing a project that person should remove themselves in a decision about it”.

“Depending on the extent of the involvement, the issue may not be just a perception of conflict or bias but actual bias, [which] would be fatal to the integrity of any decision,” he said.

“A decision-maker who has previously expressed views either for or against a proposal calls the decision into question.”

He also notes “evidence relating to the A-G’s property interests”, saying: “On the face of it there is at least the potential for conflict, or appearance of it, to the reasonable person… but it is also possible in situations like this that it gives rise to an actual conflict.”

He notes that “without further evidence the question of an actual conflict probably does not arise” but argues “the appearance of one remains an issue”.

“There is a heavy responsibility on the decision-maker to make sure there is no actual or perceived conflict before making the decision,” he said.

Sumner said the issues under consideration were “of utmost importance to good governance and the maintenance of integrity in government decision making”.

“During my time as Attorney General, I had considerable involvement in these issues including advising Premier Bannon and Cabinet in relation to an inquiry into conflict-of-interest allegations made about the Tourism Minister Barbara Wiese in 1992,” he said, noting that involved commissioning a report from Terry Worthington QC and his own submission on the principles relating to conflict of interest, prepared with the assistance of Crown Law officers including the then-Crown Solicitor Brad Selway.

He said he was also responsible for preparing a cabinet handbook, which has been in operation since 1993, which specified “how the Premier, Cabinet and Ministers should deal with conflict issues and included the Ministerial Code of Conduct”.

As part of this he proposed a code of conduct for MPs, which had not been implemented when the Arnold Government lost office in a post-State Bank 1993 landslide – and a draft for which is now under discussion by state parliament, 28 years later.

Sumner suggests it is the responsibility of Crown Law officers, including the Crown Solicitor, to “take action” if they suspect a minister is “not complying with good governance processes”.

“Where it is the conduct of the Attorney-General that is in question then the other Law Officers have to step up and deal with the issue of concern,” he said.

“In this case the A-G could not play this role because on the best interpretation the A-G had a potential and perceived conflict of interest.”

Given “some evidence” to the inquiry “of the involvement of the Crown Solicitor being in discussions with the A-G… it is desirable for the committee to clarify the role of the Crown Solicitor”.

“If these potential conflicts were made known to the other Law Officers, they should have cautioned the A-G and counselled her to comply with the Ministerial Code,” he writes.

“If the A-G refused to do so, it was the clear responsibility of the Law Officers to draw the problem to the attention of the Premier.

“With the potential conflicts that have now been exposed to the committee the Premier should have put in train the procedures in the Cabinet Handbook [and] required the A-G to disclose all the facts in relation to the conflicts, then obtained the other Law Officers’ opinion and decided based on the options in the Handbook what action should be taken to resolve the conflict, including disqualification.”

He said given “some evidence that an instrument of delegation was prepared to enable another minister to make the [port] decision… the Crown Solicitor should be able to explain this and why it was not proceeded with”.

He also urged the inquiry to hear from both the Solicitor-General and Premier’s Department boss Nick Reade, who “should be able to provide evidence of whether the process requirements set out in the Handbook were followed and if not why not”.

“I have to assume that the A-G would have been familiar with the requirements of the Ministerial Code [but] it is the Premier that has the general oversight of Ministerial conflict of interest issues,” Sumer writes.

“If the procedures were not followed, the Premier should explain why.”

In his submission, Sumner notes that “the rejected port proposal has been in gestation across two governments [and] it appears that successive ministers have encouraged the proponents to proceed”.

“No doubt considerable private funds have been expended,” he said.

“The Planning Commission recommended on balance that it proceed.”

He said while “some projects may be so unmeritorious that failing to deal properly with a conflict issue is of little consequence”, in this instance “this is not such a case”.

“The fact that so much time and money was spent preparing the project and that planning approval was recommended make it critical that the decision-making process is not sullied by conflict of interest,” his submission argues.

“It is the committee’s duty to determine whether this was or was not the case.”

Sumner urged the committee to “conduct a proper inquiry”, saying: “This is not just a simple Liberal/Labor spat.”

“The committee could not have been set up without the majority support in the House, which included independent members.”

“I agree with the House of Assembly that the committee has serious and legitimate issues to consider,” he said.

“Despite political differences it should be possible for members to come to at least substantial agreement on [what actually happened]…

“Once the facts are established the committee should seek an expert independent opinion – to ensure as much impartiality as possible I strongly recommend that this advice be sought from interstate.”

He suggested a “retired judge with impeccable independent credentials”, saying “the legal profession and academics in SA with expertise in constitutional and public law are a close- knit group [and] most will be known to each other and probably to the A-G”.