The answer lies in the regulation
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);
So a PPL holder may give instruction.
‘FCL.040 Exercise of the privileges of licences The exercise of the privileges granted by a licence shall be dependent upon the validity of the ratings contained therein, if applicable, and of the medical certificate as appropriate to the privileges exercised.
To Exercise the privileges of a PPL you need a Class 2 Medical Certificate.