The 7/7 London bombings, which killed more than 50 people in public transport and unleashed a reign of terror in the British capital, had cost only a few hundred pounds, an investigative BBC report said.
According to the investigation by the BBC World Service's Dirty Money, four suicide bombers used homemade peroxide-based bombs to mount the London attacks, which killed 52 people on three Tube trains and a bus.
The report highlights the fact that the amount of cash needed to carry out terrorist atrocities had decreased over the years, since 2001, and how hard it has become to identify terrorists by simply monitoring their finances.
While the 9/11 attacks on New York and Washington in 2001 required $500,000, the Madrid bombings in 2004 - which killed more than 190 people on the public transport system - cost less than $10,000 dollars.
Although the outlay for carrying out the London bombings was negligible, the costs of the rescue and recovery operation, along with the cost to London businesses and its tourism industry has run into many hundreds of millions of pounds, the report added.
Police began investigating the financing of the July attacks as soon as the identities of the bombers had been established.
According to the programme, police believe that one of the men, Mohammad Sidique Khan, who worked as a teaching assistant, was the principal backer of the attacks and had given money to the other men to buy some of the materials.
Speaking to the BBC, Douglas Greenburg, who studied the financing of 9/11, said, "If you have someone who is working and depositing their pay cheques into the bank and periodically withdrawing money and, at night, buying components for a bomb and constructing it in their basement, what's the bank going to do about that?"
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