The Serious Fraud Office has opened a criminal inquiry into Tata’s steel-making operation, the Telegraph can disclose.

Police officers are examining allegations that staff working for the company’s office in Britain may have falsified certificates detailing the composition of the product before they were sold.

It is understood that the inquiry centres around the group’s site in Yorkshire and arose after the company referred itself following an internal audit.

Well-placed sources said that the documents being examined affected 500 customers, including BAE and Rolls-Royce.

There is also a trading standards investigation, but it is unknown whether they are linked.

The disclosure comes at difficult time for Tata and will be embarrassing for the Government. The Business Secretary, Sajid Javid, is frantically trying to ensure that Tata acts as what he calls a “responsible seller” after the company last week said it plans to withdraw from its British steel operations, putting thousands of jobs at risk.

Last week, the Business Secretary was forced to return early from a trip to Australia when Tata announced it was putting its UK assets up for sale and Labour accused the Government of being “missing in action”.

There have been calls for the state to take temporary ownership of the plants to keep production going to retain customers, making it more attractive to potential buyers.