Well, all is not lost, but you'll need to play the long game here.
If you're using the model contract of employment for your clerk, it includes a commitment to grievance and disciplinary procedures, so if you haven't adopted them, you're in breach of the legal requirement to issue a valid contract of employment to an employee. To rectify this, propose the adoption of the NALC model grievance policy and model disciplinary policy at your next meeting to enable the council to comply with its obligations under employment law. Members will have the choice between adopting the policies or making an informed decision to break the law, something that would render them personally liable for financial penalties. Once the policies have been adopted, use them for their intended purpose.
The appraisal of all employees is an important aspect of the management role, however it comes with a caveat. Only those who have been trained in the art of appraisal should be involved in the process. You may also wish to apply a requirement for all members of an HR committee to undergo training, as this could prevent costly errors. As always, your local association should be your first port of call for such matters, but the ACAS website has some really useful resources too.