The rules do refer only to the giving of instruction for the issue of a PPL, Class or Type ratings however you can also perform instruction relating to those licenses and ratings. Continuation training, revalidation training etc.
You do not have all the privileges of a Unrestricted FI for example, you cannot do CPL training other than as part of an Integrated Course to PPL level or IR training unless you hold a standalone IRI qualification.
Any new instructor should have been taught the privileges of the rating.
The privileges of the rating are in the ANO Schedule 7
Flight instructor rating (aeroplane)
A flight instructor rating (aeroplane) entitles the holder of the licence to give instruction in flying aircraft of such types and classes as may be specified in the rating for that purpose subject to the restrictions specified below.
Restrictions - restricted period
(1) Until the holder of a flight instructor rating (aeroplane) has completed at least 100 hours flight instruction and, in addition, has supervised at least 25 solo flights by students, the privileges of the rating are restricted.
(2) The restrictions will be removed from the rating when the requirements specified in paragraph (1) have been met and on the recommendation of the supervising flight instructor (aeroplane).