The seizure of suspected U.S. bonds worth $6 billion (5.5 billion euros) by British police during a drug cartel investigation has dealt a significant blow to the cartel's operations, according to an expert on money laundering.

Working with Colombian authorities, British police came upon billions of dollars worth of bonds while conducting two raids in north London and in Essex, east of the capital.

During those searches, 13 people were arrested, nine of whom have now been charged and the rest released. In addition, several million dollars worth of cash and drugs were seized.

The British police operation took place in July and August but details were not released until Colombian authorities made the announcement on Thursday.

Officers from Britain's National Crime Squad are now in the process of determining whether the bonds are genuine. But even if not, money laundering expert Jeffrey Robinson says the bust caused real damage to the cartel.

"Because it is a business, the minute you interrupt the cash flow and reinvestment, whether it be reinvestment in real bonds through money laundering or reinvestment in counterfeit bonds, if you take the cash flow away from them, you bankrupt the business," he said. "And as soon as you bankrupt the business, you take product off the streets."

Mr. Robinson says money laundering these days is highly sophisticated and it can take many different forms.

"It is about bonds, it is about life insurance policies, it is about diamonds, it is about honey, it is about legitimate businesses," said Mr. Robinson. "The police now have the mechanism through the Proceeds of Crime Act to go after these businesses, to seize the assets and then use those assets in the furtherance of anti-money laundering activity."

In addition to the nine suspects arrested in London, two others have been detained in Colombia and two in Ecuador. The ring allegedly sent drugs from Colombia to Europe via third countries such as Mexico and Ecuador.

Colombian authorities say further arrests are expected in Europe and the investigation continues.