According to PRINCE2, a project is not considered part of 'business as usual'. The defining attributes of a project include it being a temporary organization that is created for a specific purpose, which contrasts with
'business as usual' that involves ongoing, routine activities within an organization. References: PRINCE2 Foundation manual, PRINCE2 official resources

In the 'planning' technique of PRINCE2, understanding what makes the outputs acceptable to the users occurs during the step of "Defining and Analyzing the Products." This step involves detailed discussions about product requirements and specifications to ensure clarity on what the project must deliver for it to be accepted by the users. It sets out the criteria that the products must meet to satisfy the user's needs and expectations.
References: (PRINCE27 Foundation Handbook, AXELOS)

Reference http://prince2.wiki/Quality