Class 1 is required for PPL instruction as it is 'single pilot commercial operations carry passengers' (passenger being someone under training, i.e. no licence)
Happy to be proved wrong!
WRONG! A PPL requires a Class 2 Medical Certificate and the privileges of the licence include remunerated Flight Instruction where the holder has a valid Flight Instructor Certificate
FCL.205.A PPL(A) — Privileges
(a) The privileges of the holder of a PPL(A) are to act without remuneration as PIC or co-pilot on
aeroplanes or TMGs engaged in non-commercial operations.
(b) Notwithstanding the paragraph above, the holder of a PPL(A) with instructor or examiner
privileges may receive remuneration for:
(1) the provision of flight instruction for the LAPL(A) or PPL(A);
(2) the conduct of skill tests and proficiency checks for these licences;
(3) the training, testing and checking for the ratings or certificates attached to this licence.
A student pilot is a crew member under training, not a passenger.