When you appoint a new Clerk, you provide a job description, which should ideally include some of the broader concepts, such as following the instructions of the Council, appropriate conduct, etc. This would normally appear in your person specification in the recruitment pack, but can be in both documents. You should also provide a contract of employment, preferably the NALC model. This contract requires the Council to provide the Clerk with a copy of the Council's grievance and disciplinary policies, amongst others. The NALC model disciplinary policy provides a list of examples of misconduct and of gross misconduct, as well as unsatisfactory work performance. These lists cover most of the issues raised on this forum in relation to the conduct of a Clerk. All of the above accords with the National Agreement (the Green Book).
The other policies you require for a new Clerk are health & safety, equal opportunities, expenses and sickness absence, all of which are mentioned in the model contract.