Hitting back at Tata Sons director Vijay Singh, ousted Chairman Cyrus P Mistry on Sunday accused the former of playing a key role in the alleged Rs. 3,600 crore AgustaWestaland chopper scam.

Singh, who is serving as the director of the conglomerate, had served as the Defence Secretary to the Government of India.

"It's amusing to see Vijay Singh concoct theories to defend his role in Ratan Tata's conspiracy to replace Cyrus Mistry," Mistry's office said, while adding, "As defence secretary Vijay Singh was a key official involved in the award of the Rs 3,600 crores VVIP helicopter contract to AugustaWestland in 2010. It is a matter of public record that the government had to cancel the contract, dubbed "Choppergate" by the media, due to charges of corruption and graft," it added.

Mistry said Ratan Tata in 2010 had set up a Joint Venture with Italy-based Finmeccanica's helicopter unit AgustaWestland, called the Indian Rotor Craft (IRL), to manufacture AW119 utility helicopters.

"Media reports indicate that the assembly line envisaged in this JV would address part of Finmeccanica's offset obligation arising from the sale of the now cancelled VVIP helicopters," he said.

Mistry said after the retirement of Ratan Tata, on his instructions, Vijay Singh was invited to join the Tata Sons Board in 2013 as a nominee of the Tata Trusts.

"It is a matter of record that Ratan Tata travelled to Italy to 'voluntarily depose' for Finmeccanica's chief Guiseppe Orsi as a defence witness in 2014. Incidentally, in April this year, an Italian court sentenced Orsi to jail for false accounting and corruption over the sale of the 12 AugustaWestland helicopters to India," he said.

Mistry also claimed that Vijay Singh, who was a member of the Nominations and Remuneration Committee (NRC) of Tata Sons on June 28, 2016, gave a glowing review of the performance of Mistry as Chairman of the Group.

"After reviewing the performance of the Executive Chairman, the members unanimously recorded their recognition of his significant contributions across Group companies and expressed their appreciation of his multi-faceted initiatives aimed at preserving and promoting cohesive functioning of the Group in accordance of its distinctive values," he added.

"In fact, Vijay Singh also stated that Tata Motors have come up with some of their best models in recent years. His colleague Ronnen Sen, an independent director, also added that from his experience, Mistry had earned the respect of not only CEOs and senior management but also operational personnel," he added.

Mistry said with regards to Welspun, Singh, as a Trust Nominated Director, explicitly supported this strategy when a note on the topic was circulated amongst the Board members. Later, he along with Nitin Nohria, had to leave the Board Room for over an hour to take instructions from Ratan Tata on how to articulate his mind on the Board deliberations. Perhaps he needed guidance on how to overcome his past excitement in favour of the transaction.

Mistry also pointed out that Singh's compensation increased from Rs. 90 lakhs to Rs. 1.3 crores over the last year, an increase of nearly 45%, whereas in the same year Mistry restricted his pay increase to 6%.