Although this is entitled get ready for your mid year it also has the details in about challenging any unfair marking:
Dispute unfair ratings
It is best practice to try to resolve disputes informally and only resort to formal action as a last resort. However, you can raise a formal grievance and appeal under People Performance Procedure13 but you must put your case for Management Investigation on form G1 within 30 working days of the original decision (Grievance Procedure 5.7). You may contact your local PCS Representative for advice, support and representation.
Please click here for further details:
PCS Fylde 