Singh was speaking alongside British Prime Minister David Cameron, who is on a three-day visit to India to push trade ties amid a corruption row over a $750 million deal for a dozen AgustaWestland helicopters.
"I also conveyed to the Prime Minister our very serious concerns regarding allegations about unethical means used in securing the 2010 contract of the AgustaWestland helicopters," Singh said.
"I have sought full assistance from the UK in this case. Prime Minister David Cameron has assured me of the cooperation of his government in the investigation."
Cameron, speaking after Singh, said his government would respond to any request for information about the deal.