In order to be listed on CIMA's member in practice register you must hold a current practising certificate.
If you receive no payment for your work it is not necessary for you to register (see CIMA's member in practice regulations). However, If you are providing any reporting services, such as signing off accounts as an examiner, you should consult with the relevant standards of reporting practice. Please visit the regulators page for further guidance.
Even if working in an honorary capacity, you may still be legally liable for incorrect work. You should therefore ensure you are able to complete any work undertaken and may wish to gain professional indemity insurance.
Note that charitable companies are subject to a lower audit threshold than other companies. You'll find more on the members and audit page.