Two dozen firms that deal with high-risk digital currencies such as Bitcoin are being probed by the City watchdog.
The 24 companies face inquiries by the Financial Conduct Authority into whether they traded without the proper authorisation.
Probe: The FCA is also looking into seven complaints by whistleblowers raised this year about the digital currency dealing industry
The FCA is also looking into seven complaints by whistleblowers raised this year about the industry.
It comes amid a crackdown on so-called cryptocurrencies, with regulators worldwide warning that investors could lose everything in the Wild West market.
The FCA, the Bank of England and the Treasury are now reviewing the crypto market and could introduce new rules.