Organic is a regulated activity, so the requirements for organic production, including separation and segregation, are laid out in law. In the UK, that is currently a retained European regulation, No. 834. That mandates an inspection and certification system based on international norms for product certification. The way in which producers who are under the control system specified in the regulation notify their activity and interaction with independent third-party certifiers, such as Organic Famers & Gowers and the Soil Association, is described in that regulation.
It is very much a farm-to-fork regulation: it covers all parts of the production process, from the farm, beyond the farm gate, right through to the point of sale. There is complete traceability, which is overseen by the certification bodies and maintained through record keeping and some elements of testing and checking, which are carried out both by those who are subject to the regulation and by the certification bodies that oversee their activity.