A top Visa executive has launched one of the most outspoken attacks yet from the financial establishment on the bitcoin craze, saying cryptocurrency was used by "every crook and dirty politician" and speculators who have "no clue."

In an interview with the Financial Times, Vasant Prabhu, chief financial officer of the world's biggest payment network by market value, recalled encounters he had with ill-informed retail investors that had been "a real shock" to him."

"The people asking me are the ones who scare the hell out of me," he said. "You know, guys like the limo driver to the airport . . . They have no idea what they are doing."

Visa operates at the heart of the mainstream global payments system, connecting about 3bncard holders, 46 m payment locations and 17,000 financial institutions.

Recognising the strength of feeling among crypto aficionados who wish to circumvent financial institutions, Mr. Prabhu said he lived not far from "true believers" in Silicon Valley who think"people like me are dinosaurs".A bank teller told Mr. Prabhu about six months ago how he planned to sell bitcoin in March,because he knew that was when the price would peak. A young member of Mr Prabhu's extended family enthused over a Thanksgiving dinner that an $8,000 crypto investment he made had doubled in value.

"This is the ultimate thing that you hear about when you have a bubble, when the guy shining your shoes tells you what stock to buy," the Visa executive said.

Bitcoin has collapsed from a pre-Christmas high above $19,000 to trade at about $8,100 but it is still up eight-fold from the start of last year, according to Bloomberg data.

Some of Mr. Prabhu's peers on Wall Street have become wary of speaking out. Jamie Dimon, head of JPMorgan Chase, said last month he regretted describing bitcoin as a "fraud" — not because he had changed his mind, but because it had become all anyone wanted to talk to him about.

Visa, which has a market capitalisation of $279bn, has been peppered with questions from analysts and investors about whether its model will be disrupted by emerging payment systems.

So far, it appears to have shrugged off any potential threat. Shares are up more than 1,000 per cent since its initial public offering 10 years ago next week, helped by the digitisation of global payments.

The San Francisco-based group is experimenting with the technology that underpins cryptocurrencies. It is trialing a blockchain-based platform for banks to facilitate cross-border corporate payments.

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However, the company does not process or settle transactions in cryptocurrency itself. "With a currency issued by the Federal Reserve, I know who stands behind it," Mr. Prabhu said. With cryptocurrency, he said: "Who's good for the money? Who the hell knows?

"Visa does not block consumers from using its network to buy cryptocurrency, although severalbanks that issue its cards have implemented such a ban.

The company also went to great lengths to comply with know-your-customer and anti-money laundering rules, Mr. Prabhu said. "We shut people down immediately where we have even thewhiff" of wrongdoing, he added.

In contrast, he said, cryptocurrencies were a "favourite" for criminals. "It's very hard to get dirty money through a banking system. Cryptocurrency is phenomenal for all that stuff . . . Every crook and every dirty politician in the world, I bet, is in cryptocurrency."

Chris Skinner, a financial technology author, said it was "complete rubbish" to suggest the main use of cryptocurrencies was criminal. "There is some criminal activity associated with some cryptocurrencies but it is quite minimal," he said. "It's a myth that the financial community want to promote."

Mr. Prabhu said: "My personal view is that cryptocurrencies are more speculative investment commodities than payment options, operating in a very unsettled regulatory environment. The markets are testing cryptocurrencies today with the volatile fluctuations we've seen recently. It's early days and we'll watch it very closely."