Global Financial Integrity , a Tax Research UK partner in the Task Force on Financial Integrity and Economic Development have reported:

“The Drivers and Dynamics of Illicit Financial Flows from India: 1948-2008,” released this week by Global Financial Integrity (GFI), estimates that tax evasion, crime, and corruption have removed gross illicit assets from India worth US $462 billion over 60 years

As they put it:

"From 1948 through 2008, India lost a total of US $213 billion in illicit financial flows (or illegal capital flight). These illicit financial flows were generally the product of: tax evasion, corruption, bribery and kickbacks, and criminal activities. The present value of India’s total illicit financial flows (IFFs) is at least US $462 billion (based on the short-term U.S. Treasury bill rate as a proxy for the rate of return on assets.) India’s aggregate illicit flows are more than twice the current external debt of US $230 billion.

The full report is available here.