The Tasmanian government department investigating the deaths of polo ponies on board the Spirit of Tasmania has refused to provide any information about the incident under right to information (RTI) laws because it would not be "in the public interest" and could prejudice a trial.

Former national team captain Andrew Williams was driving the truck. ( Supplied: Willo Polo )

The Department of Primary Industries, Parks, Water and the Environment (DPIPWE) has refused the ABC's request for all material related to the January deaths of the polo ponies.

The ponies died on a horse float which had been driven by the former captain of the Australian polo team and national polo identity Andrew Williams, and was crossing Bass Strait after competing at Tasmania's premier polo event.

Mr Williams is suing the ferry operator TT-Line for negligence and has lodged a writ in the Victorian Supreme Court.

RTI expert Rick Snell said it appeared the department was "stonewalling" by refusing to provide any material, and had failed to even indicate what type of information — for example, emails or autopsy reports — was being withheld.

The refusal asserts that it would not be in the public interest to release the information, and could prejudice either the investigation or a fair trial in relation to the case if the information is released.

Adjunct Associate Professor Snell said he did not believe it was a fair use of RTI provisions to refuse the information on the basis that it could be prejudicial, because the likelihood of a jury trial was low.

One of two Willo Polo trucks carrying ponies boards the Spirit Of Tasmania on January 28. ( Instagram: chelcroz )

Public interest 'box ticked'

The public interest test in Tasmania's RTI Act includes 25 different provisions that a RTI officer can consider in favour of, or against, the release of information depending on their relevance to the material being considered.

Professor Snell said in this case, only one of the provisions in favour of release was weighed up — the general public need for government information to be accessible — against three in favour of refusal, which he said effectively "ticked the box" as having been considered.

Rick Snell says the decision appeared to only minimally apply the public interest. ( ABC News )

"In terms of all the particular types of public interest outlined in schedule one [of the RTI Act], they chose the most vague, most general principle to look at and weighed that against the reasons not to disclose," Adjunct Associate Professor Snell said.

"It's like weighing a scale where you put your fingers on one side of the scale that tips it against you … there's a number of other factors which the public are well aware of why the release of this information could be in the public interest."

The decision was made by department secretary John Whittington, which means it cannot be internally reviewed.

Only the ombudsman can review the RTI application, but those reviews can take years to complete due to a significant backlog.

Adjunct Associate Professor Snell said it was highly unusual for the head of an agency to process an initial RTI request.

"Normally it's handled by a right to information officer whose decision is then subject to a review. It's highly unusual for the head of an agency to conduct an original review," he said.

"I think the primary objective was to stonewall [the ABC's] application process."

Action from the Barnbougle Polo competition, in north east Tasmania, in January. ( Facebook: Barnbougle Polo, file )

Public being kept in the dark: vet

Equine veterinarian Michael Morris said the State Government was keeping the public in the dark.

"We have Mr Williams claiming his ponies died as a consequence of things that transpired of Sprit of Tasmania, and it is clearly in the public interest to know whether that is the case or not," he said.

The Spirit of Tasmania operator TT-Line, which is a state-owned company, is being sued for negligence over the deaths of prized polo ponies on board in January.

The civil claim, seen by the ABC, alleges 13 ponies died between boarding the ferry at Devonport for the 7:30pm departure to Melbourne and about 2:00am.

The Department of Primary Industries, Parks, Water and the Environment has been investigating the deaths.

The Department said the RTI process was independent and the decision could be reviewed by the ombudsman.