The pair, aged 38 and 44, were questioned and released on bail after a search of their offices in the capital, the Financial Conduct Authority said.
Two people have been arrested on suspicion of running an illegal exchange thought to have traded more than £1bn worth of cryptocurrency.
The Financial Conduct Authority (FCA) searched the London offices of the suspects, aged 38 and 44, while the Metropolitan Police seized digital devices from two residential properties in the capital.
More than £1bn worth of unregistered crypto assets are believed to have been bought and sold through the exchange.
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Both suspects were interviewed under caution before being released on bail and the FCA says its investigation into the case was ongoing.
Therese Chambers, executive director of enforcement and market oversight at the FCA, said: “The FCA has an important role to play in keeping dirty money out of the UK financial system.
“These arrests show we will do everything in our power to stop crypto firms from operating illegally in the UK.”
The arrests follow a recent global crackdown on crypto companies after the collapse of some of the biggest firms in the sector, leading to millions of people losing money they had invested in cryptocurrencies.
The high-profile implosion of FTX, the crypto exchange run by Sam Bankman-Fried, saw the mogul sentenced to 25 years in prison in the US for defrauding customers and investors.
Meanwhile, Changpeng “CZ” Zhao, the founder of crypto exchange Binance, was sentenced to four months in prison in April for allowing criminals to launder money on his platform.
Zhao, who resigned from Binance in November, pleaded guilty to breaking US money laundering laws.
Binance is still operating and remains the biggest crypto exchange in the world by transaction volumes.
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The FCA has a register of so-called authorised crypto companies which are allowed to operate from the UK.
Currently, the list numbers 45, including crypto spinoffs set up by financial giants such as Fidelity, Standard Chartered, and Japanese investment bank Nomura.
But a separate list of crypto companies the regulator suspects of operating illegally in the UK has more than 13,000 businesses on it.
The FCA also forces registered crypto firms to prove they comply with UK money laundering regulations in order to operate legally.