Payment
You cannot be paid to act as pilot or as an instructor unless you hold a CPL. There are a few exemptions from this restriction that have been granted just the same.
A Non-CPL Instructor may be paid when instructing for the Microlite Licence and other similar NPPL licences by grant of an exemption. Unfortunately no such exemptions have yet been granted for teaching the PPL 'A', be it for the NPPL or EASA PPL.
However, should you hold a Flight Instructor Rating but not a hold a CPL or valid CPL (ie no current Class 1 medical) you may instruct unpaid. A flying club could come to an arrangement whereby they employ an instructor for one task and pay for that work but require the same person to do any flight instructing without pay. It would be necessary to ensure that it couldn't be construed that any payment for another different task was in fact a substitute for the flight instructing work.