The Financial Services Authority (FSA) has confirmed that the 30-month rule applies to most Retail Distribution Review (RDR) activities.
In its latest RDR newsletter, the regulator said a number of firms had sought a clarification on the rule.
It said: "The 30-month rule applies to most but not all RDR activities. We expect this will only impact a small number of individuals but please contact us if this causes any concern.
"For most activities, a retail investment adviser must attain an appropriate qualification within 30 months of starting to advise.
"The 30-month rule does not apply to advisers who intend to both advise on and deal in securities and derivatives because they cannot start these activities until they have completed all of the modules of their qualification."
While advisers deemed competent by their firm before or on 30 June 2009 will have to achieve an RDR appropriate qualification by 31 December 2012, under the 30-month rule, registered individuals deemed competent after 30 June 2009 will not need to meet the same deadline.
Instead, they have 30 months from 1 January 2011 or, if later, 30 months from the date that they started the activity of advice to attain an appropriate qualification.
In the meantime, they can operate as a trainee adviser under suitable supervision, advising on retail investment products or advising on securities and derivatives, as long as they have attained the regulation and ethics module of an appropriate qualification.
However, advisers who intend to both advise and deal in securities and derivatives cannot start this activity until they have completed all of the modules of their qualification.