The information commissioner, who is responsible for enforcing the Data Protection Act, is investigating the arrangement, which has seen details of computerised transactions from around the world passed to the CIA in an attempt to spy on the financiers of jihadist terrorism.

The US government has acknowledged that the agency has been receiving international financial records from the Belgian-based co-operative which processes money transfers on behalf of the world's banks. The programme was launched in the wake of the September 11 attacks.

Data handed over each year by the Society for Worldwide Interbank Financial Telecommunication, or Swift, includes the details of an estimated 4.6 million British banking transactions.

A spokesman for the information commissioner told the Guardian that the privacy issue was being taken "extremely seriously". If the CIA had accessed financial data belonging to European individuals then this was "likely to be a breach of EU data protection legislation", he said, adding that UK data protection laws may also have been breached if British banking transactions had been handed over. The commissioner is requesting more information from Swift and the Belgium authorities before deciding how to proceed.

The Bank of England, one of the 10 central banks with a place on Swift's managing committee, revealed it had told the British government about the programme in 2002. "When we found out we informed the Treasury and passed the relationship over to them," Peter Rogers of the Bank said. "We also told Swift that they had to speak to the government themselves. It had nothing to do with us. It was a matter of security and not of finance. It was an issue between Swift and the government."

In a written parliamentary answer, Gordon Brown last month confirmed the government was aware of the arrangement. Citing government policy not to comment on "specific security issues", however, the chancellor refused to say whether measures had been taken to "ensure the privacy of UK citizens who may have had their financial transactions viewed as part of US counter-terrorism investigations in conjunction with Swift". He also refused to say whether the Swift programme was "legally reconciled" with Article 8 of the European convention on human rights.

Vincent Cable, the Liberal Democrat Treasury spokesman who tabled the questions, said: "This feeble response shows the chancellor is taking refuge behind national security. I'm not asking for sensitive security information on individual cases, but for a reassurance that the collaboration with the US was lawful."

A Home Office spokesman said the government had been given "no reason to believe the operation was unlawful", adding that it "strongly supports US efforts to target, disrupt and cut off sources of funding for terrorism". He declined to comment on the commissioner's assessment that the programme may be illegal.

Under US law, the legal basis for eliciting information from Swift was "absolutely clear," according to Stuart Levey, the under secretary for the Office of Terrorism and Financial Intelligence.

But concerns over the potential for abuse were heightened when the US Treasury later admitted that at least one search had been carried out "inappropriately". "The person who conducted that search is no longer allowed to work on this programme," a spokesman said.

In a statement, Swift said that it had acted in response to legally issued subpoenas. "Our fundamental principle has been to preserve the confidentiality of our users' data while complying with the lawful obligations in countries where we operate," it said.

Guardian Unlimited © Guardian Newspapers Limited 2006

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