The Financial Services Authority (FSA) is reminding businesses they must be registered, or face a hefty fine.
A spokesman said businesses such as accountants, crypto companies and estate agents must be registered with the Authority.
Failing to do so could mean a fine of up to £5,000.
The FSA warning comes after a number of firms promoting or performing services they aren't registered to do.
The offence has resulted in action against five companies in two years, with penalties totalling £20,000.
Anyone starting a new business is encouraged to speak to the Financial Services Authority for the latest advice.
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