Britain's financial watchdog plans to tighten scrutiny of banks, trade financiers and high-risk investment funds in what a senior official concedes is a near-impossible battle to intercept terrorist funds.
Philip Robinson, head of the crime division at the Financial Services Authority (FSA), said the increased supervision was needed to counter the increasingly inventive ways in which militants were laundering dirty money.
"I don't think it is possible through the normal anti-money laundering regime to spot terrorism finance," Robinson said in an interview with Reuters.
"It is very possible for this to be going on and for it to be very difficult to detect."
Since the September 11, 2001, attacks, financial authorities have sought to identify and seize so-called dirty money that could be used to fund atrocities.
But experts are increasingly sceptical, saying relatively small amounts of money - sometimes carried across borders as cash - could suffice to mount attacks.
Robinson and other law enforcement authorities say that criminals and terrorists are becoming increasingly inventive. He said the cash from crime that does not pile up in basements or leave Britain in shipping containers was being laundered in part through the financial sector.
"It's going out through the financial services industry. I know it is. I just don't know where," he said.
As a result, the FSA aimed to broaden its examinations of financial firms to close off possible escape routes for the dirty billions.
The trade finance sector, used to process import and export transactions, was one area to target. The gambling sector was another. "You can walk into a casino with cash and walk out with a check," he said. "It's not a lost cause. What we have to do is find a way to narrow the channels."
Stock brokers and insurers were now viewed as possible money laundering channels, he said.
Even hedge funds, the unregulated investments housed frequently in offshore centres, can also expect to come under scrutiny, Robinson said, primarily because they have quickly grown to become an important part of the financial industry.