55.This section contains the basic prohibition on unauthorised persons carrying on regulated activities in the United Kingdom.  It is referred to in the Act as “the general prohibition” and prohibits persons who are not authorised or exempt under Part III from carrying on any regulated activity in the United Kingdom.  Section 418 elaborates on when regulated activities will be considered to be carried on in the United Kingdom.  Contravention of the general prohibition is a criminal offence (see section 23).  Agreements made in the course of carrying on an activity in contravention of the general prohibition may be unenforceable (see sections 26, 27 and 29).
Commentary on Sections Part Ii: Regulated and Prohibited Activities Section 19: The general prohibition