Section: Volume B

A feature of a stage plan that suggests a project is in danger of scope creep is when products identified in the stage plan cannot be traced back to the project plan. This indicates a lack of alignment between the stage and overall project objectives, potentially leading to uncontrolled changes or additions to the project scope, known as scope creep.
PRINCE2 7 Foundation documentation on stage planning and scope management.

Section: Volume B

Stage Plans in PRINCE2are essential tools for the Project Manager, assisting in the day-to-day management and control of the project. Each Stage Plan provides the detail needed for each management stage of the project, including what work will be done, when it will be delivered, and who will be involved, thus facilitating effective project governance on a stage-by-stage basis. They do not necessarily match the duration of the Project Plan or get produced simultaneously with the Project Initiation Documentation.
References: PRINCE27 Foundation handbook and other official documents.