The Bank of England told HM Treasury about the secret US surveillance of international banking transactions as long as five years ago.
The US's eager pursuit of terrorist financiers, begun within weeks of the 11 September attacks, involved a trawl through the world's financial transactions through subpoenas on the firm that handles them for private banking clients - the Society for Worldwide Interbank Financial Communication (Swift).
European authorities, including the UK's Information Commissioner, have since declared the US operation "illegal" and have begun to press financial institutions to put a stop to the warrantless and unprotected transfers of private banking data to the US authorities.
This programme remained a secret from privacy watchdogs - even from those people whose data was being handed over to US investigators - until the New York Times unearthed it last June. Yet HM Treasury knew about it for some years.
A spokesman for the Bank of England told The Register: "Swift told us in 2002 that it had agreed with the US subpoenas. We told Swift it should tell the government. We told HM Treasury. We felt they should know."
The G10 central banks, which act as Swift's oversight board, were told about the subpoenas in February 2002, European Central Bank (ECB) president Jean-Claude Trichet told the EU Parliament in October.
But the ECB had decided not to warn "other relevant authorities" about Swift's decision to give US authorities access to its international banking transactions because it believed its own responsibility for "professional confidentiality" among its members was more important.
Other European authorities like the European Data Protection Supervisor might not have been informed, but more European governments might have been aware of the illegal data trawl than just the British.
A source involved in the ongoing European investigations told The Register: "As far as I understand, some central banks I know decided to tell their governments. I've been told that it was a few countries."
The European Parliament passed a resolution this week that stated its concern that the US trawl of EU financial data had gone on so long in violation of "European and national data protection legislation" and without the proper authorities being informed.
It told the European Commission to find out if systems such as Swift's made it easier for foreign governments to commit industrial espionage at the expense of European firms. No specific reference was made to the US Treasury's subpoenas on Swift in this regard, but the example being used on the street in Brussels is Airbus.
It also endorsed the opinion of the European Data Protection Supervisor who two weeks ago said the ECB should be concerned about the privacy because if people thought their transactions weren't secure they might lose confidence in the financial system.