An investigation by the ABC's Four Corners program has uncovered previously unknown tax haven ties for Adani Group's Australian operations, with key assets ultimately owned in the British Virgin Islands.

Key points: Adani Group's filings with ASIC fail to mention a company registered in the British Virgin Islands

Adani Group's filings with ASIC fail to mention a company registered in the British Virgin Islands Vinod Adani, older brother of Adani Group chairman Gautam Adani, has been under investigation in India

Vinod Adani, older brother of Adani Group chairman Gautam Adani, has been under investigation in India Vinod Adani also a substantial shareholder in Adani Enterprises Limited

Adani Group has promised a $22 billion windfall in taxes and mining royalty payments for Australia over the life of the giant Carmichael coal mine it has been given approval to build in outback Queensland.

But experts say an opaque web of companies and trusts behind its Australian assets gives it ample opportunity to minimise the tax it pays.

"Absolutely, Adani has put in place multiple ways in which they can minimise the amount of tax they pay in Australia, and maximise the amount of profits if they choose in Caribbean tax havens," Adam Walters, research director at the consultancy Energy and Resource Insights, told Four Corners.

Adani Group's assets in Australia include the Abbot Point Coal Terminal near Mackay in Queensland, a terminal expansion project it has approval to undertake at Abbot Point, and a planned railway line of nearly 400 kilometres from the port to the giant mine it wants to build in the Galilee Basin — aided by a subsidised loan of up to a $1 billion it is seeking from the Federal Government's Northern Australia Infrastructure Facility.

It was previously thought that Atulya Resources, a Cayman Islands domiciled company controlled by members of the Adani family, was the ultimate holding company for Abbot Point, the expansion project, and the railway.

However, filings in Singapore by privately-owned Adani companies show that a company registered in another notorious tax haven, the British Virgin Islands, sits behind Atulya Resources.

Abbott Point Coal Terminal near Mackay in Queensland. ( Four Corners: Stephen Long )

Vinod Adani investigated over alleged scam

It is variously described in the offshore company filings as ARFT Holding Limited, AFRT Holding Limited and Atulya Resources Family Trust.

Adani Group's filings with Australia's corporate watchdog, ASIC, fail to mention this company, instead continuing to list Atulya Resources as the owner.

The British Virgin Islands' company's apparent position at the apex of the structure is disclosed in the financial reports of a series of Adani companies controlled by Vinod Adani, also known as Vinod Shantilal Adani or Vinod Shah.

Vinod Adani, the older brother of Adani Group chairman Gautam Adani, has been under investigation in India over an alleged scam designed to shift money offshore.

Vinod Adani, the older brother of Adani Group chairman Gautam Adani, has been under investigation in India. ( Four Corners: Stephen Long )

Investigating officers from India's Directorate of Revenue Intelligence accused Vinod Adani, along with ex-Adani Group employees and Adani companies, of executing a "planned conspiracy of siphoning off foreign exchange abroad ... and Trade Based Money Laundering".

But the case was recently quashed by an adjudicator.

After hearing Adani Group's defence, he ruled in late August that the transaction between Vinod Adani's companies and subsidiaries of Adani Enterprises was at "arms' length" and on legitimate commercial terms.

Adani Group told authorities that Vinod Adani, as a non-resident Indian domiciled in Singapore, was an independent businessman with "no involvement" with the Adani group of companies.

However, Vinod Adani's intimate involvement in the ownership structure of Adani's Australian operations casts doubt on that claim.

Vinod Adani is the sole director of a number of Singapore-registered companies that control the Australian rail and port assets and are in turn owned first in the Cayman Islands and then in the British Virgin Islands.

Potential to shift billions of dollars offshore

The Adani Groups assets include a terminal expansion project it has approval to undertake at Abbot Point. ( Four Corners: Stephen Long )

"I think there's a national security issue here," energy finance analyst Tim Buckley, a long-time critic of the Carmichael mine, said.

"[Abbot Point] one of our biggest ports, it's owned in this opaque structure through multiple tax havens," he said.

"The sole director in Singapore is Vinod Shah and Vinod Shah is under multiple corruption and tax fraud inquiries by the Indian Government, and yet here we are with the port, one of the biggest ports in Australia controlled by Vinod Shah."

Adam Walters said: "I think if I was the Australian Government, and I was considering giving a $1 billion loan to enable a rail project, I would be very concerned by what appears to be a corporate structure that is designed to maximise profits in tax havens and has as a sole director of the intermediate companies, somebody who has been under investigation for very serious financial offences in India."

Adani Group's Australian operations ultimately owned in Caribbean tax havens. ( Four Corners )

Vinod Adani is also a substantial shareholder in Adani Enterprises Limited, the ultimate owner of the Carmichael mine.

Another previously unknown British Virgin Islands-based entity provides a potential conduit for the Adani Group to shift potentially billions of dollars from its Australian operations offshore.

Carmichael Rail Australia Ltd BVI, registered in the British Virgin Islands, appears to directly control trusts established for the railway project in Australia.

One of those trusts is eligible to receive an "overarching payment" of $2 a tonne from the coal extracted from the Carmichael mine, rising by inflation for two decades. Carmichael is licensed to mine 60 million tonnes of coal a year.

Adam Walters says this gives Adani Group multiple ways to "skin it" and move revenue to the Caribbean: "Either to the Cayman Islands via Singapore or directly to the notorious tax haven of the British Virgin Islands".

Specialist tax lawyers and bankers who spoke to Four Corners say there is nothing unlawful about the structure Adani has established for its Australian operations.

All observed that it could have legitimate non-tax purposes, such as ease of asset disposal, and ease of bringing in other investors to their operations.

But experts also commented that it would provide opportunities to — lawfully — make the entire venture highly "tax effective".

One suggested the prospect of the project paying $22 billion in taxes and royalties was somewhere between "Buckley's and none".