The Financial Conduct Authority, in co-operation with the National Crime Agency and Kent police, has arrested one man in relation to a boiler room fraud.
The 21-year old’s arrest and interview follows the regulator’s execution of search warrants at addresses in London and Kent.
No further details have been released and no individuals have been charged.
Because high-pressure mass sales operations - also known as boiler rooms - often involve people selling next to worthless shares without FCA permission, they constitute unauthorised business.
Conducting unauthorised business is a criminal offence punishable by up to two years in prison, a fine, or both, the FCA said.
Making misleading statements is punishable by up to seven years in prison, a fine, or both.
In September 2013, the City of London Police arrested six men as part of an investigation into a suspected boiler room fraud selling carbon credits in the City.