The price of digital currency Bitcoin has fallen by 20% in a period of wild trading since it passed the $11,000 mark a day ago.
Bitcoin is now around $9,150, down sharply from the record $11,434 (£8,500) it hit on Wednesday.
At its peak, Bitcoin had increased by 1,000% from the $1,000 value at which it started the year.
On Wednesday, a Bank of England deputy governor warned "investors should do their homework" on Bitcoin.
Unlike traditional currencies, Bitcoin is not issued by a central bank or government.
Bitcoins are created through a complex process known as mining, and then monitored by a network of computers across the world.
A steady stream of about 3,600 new Bitcoins are created a day - with about 16.5 million now in circulation from a maximum limit of 21 million.
Despite its price rise, Sir Jon said Bitcoin was "not of a size that would be a threat to financial stability" or a risk to the UK economy.
Financial regulators have taken a range of views on the status of digital currencies and their risks.
US regulators have moved towards treating some of them as currencies, whereas Korean regulators see them as commodities.
The UK's Financial Conduct Authority warned investors in September they could lose all their money if they buy digital currencies issued by firms, known as "initial coin offerings".
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