If you have a personal contractual relationship with the Council, employment law would consider you to be an employee, albeit unpaid. The Council should have a grievance procedure for employees, so you may wish to submit a grievance under that policy.
If the Council has adopted the model standing orders, there is a paragraph (19d in the current model) that sets out the grievance process as follows:
"Subject to the Council’s policy regarding the handling of grievance matters, the Council’s most senior member of staff (or other members of staff) shall contact the chairman of the Council in respect of an informal or formal grievance matter, and this matter shall be reported back and progressed by resolution of the Council."
The Clerk's line manager would normally be the Staffing Committee of the Council, so any complaint should be submitted to the Chair of that Committee.
Details of all of the above policies and procedures should be published on the Council's website.