Police are investigating allegations staff tampered with certificates detailing the composition of the steel products before they were sold.
Reports say the company’s Yorkshire site is the focus of the inquiry. At least nine employees have been suspended and around 500 clients, including BAE and Rolls Royce, are thought to be affected.
There is also a trading standards investigation, but it is unclear whether it is linked to the criminal investigation.
Tata Steel announced it had put its entire UK business up for sale following a board meeting in Mumbai, putting thousands of workers’ jobs at risk,most at plants in Scunthorpe and Lanarkshire.
The company said the move was to stem heavy losses from high manufacturing costs, competition with China, and a global oversupply of steel.
Ratan Tata, the former chairman of Tata Group, defended the decision, calling the UK operation under-invested and overmanned.
Liberty House owner Sanjeev Gupta has emerged as the most likely buyer of Tata Steel UK. He said the deal would require a partnership with the Government.
Business secretary Sajid Javid said Tata Steel intends to formally begin the sale process by April 11.