Bitcoin billionaires are no longer worth so much after a significant sell-off left their values tumbling.

Forbes published their first ever cryptocurrency rich list last week - but it is already hopelessly out of date, following a mass sell-off of cryptocurrencies which left prices at their lowest levels for months.

Chris Larsen, co-founder of the Ripple currency, and Cameron and Tyler Winklevoss, best known for suing Mark Zuckerberg for $65 million after claiming he stole their idea for a social networking site to start Facebook, were three of the big billionaire names in the top 10.

The Winklevoss twins claimed in 2013 that they owned 1% of all Bitcoin in existence, and it was reported in December 2017 that they had holdings worth around $1.3 billion. They had used their funds from the Facebook lawsuit to start buying up Bitcoin when it was less than $10 per coin.

However, Bitcoin has now slumped to more than half of its December peak value, when it had reached almost $20,000. After tumbling in January, Bitcoin's value plunged further from $10,000 to $6,000 in just four days at the start of February, though it has since stabilised slightly at around $8,100.

Ethereum co-founder Joseph Lubin, Binance chief executive Zhao Changpeng and investor Matthew Mellon were the other names making up the top five in Forbes' rich list who will have since seen their billions slump. However, it is thought amateur investors will be more badly hit than the billionaires who are now still at last millionaires.

Part of the reason for the slump in digital currency prices is thought to be that regulators and banks have begun taking action to protect consumers. Lloyds Banking Group in the UK recently banned customers from buying Bitcoin on their credit cards, while Citigroup, Bank of America and J P Morgan Chase in the US all did the same last month.

The sharp swings in the value of cryptocurrencies have sparked fears that buyers could be running up unsustainable debts with banks footing the bill should prices continue to fall.

"We continually review our products and procedures and this is part of that," a Lloyds spokesperson said.

Prime Minister Theresa May warned in January that action against digital currencies might have to be taken. "In areas like cryptocurrencies, like bitcoin, we should be looking at these very seriously," she said.

"Precisely because of the way they are used, particularly by criminals."