The Defence Ministry did not stick to the rules from the beginning to the end, the report said. Several instances were observed in which the ministry "deviated from the 2006 Defence Procurement Procedure".

The specifications of the choppers, meant for use by top politicians, including the Prime Minister, were altered, "leading to restricted competition and ultimately a single-vendor situation," the top auditing body said.

During the tendering process, the cabin height requirement was increased by 1.8 m. The flying height of the choppers was reduced from 6,000 ft to 4,500 ft, making AgustaWestland the only eligible vendor, the CAG report said.

A higher base price had been set for the purchase of the helicopters, which provided no "realistic basis for obtaining an assurance about the reasonableness of the cost of procurement of AW101 helicopters," the report said.

The reports said contrary to the practice of conducting chopper flying trials at home, former Air Force Chief Fali Major decided to do it abroad.

The Air Force never tested the AW-101 chopper. Field trials of the AgustaWestland chopper were conducted on representative helicopters -- Merlin MK-3A and Civ-01 and on a mock-up of the passenger cabin, the CAG said.

Three helicopters were delivered to India before the deal ran into trouble in February 2013.

As the bribery scandal unfolded, beginning in Italy, India froze payments to the company. AgustaWestland denied any wrongdoing and asked India to pay the due amount. In 2012, three of the promised 12 choppers were delivered.

The CBI is questioning Fali Major's predecessor, former Air Marshall SP Tyagi, who allegedly received kickbacks for influencing the deal in favour of AgustaWestland. Mr Tyagi has denied the allegations.