In the case of holdings which consist of two or more separate flocks, the competent authority may, in accordance with criteria set by the Commission under the procedure laid down in Article 25, grant a derogation from the requirements of Article 5 (1), for healthy flocks of a holding which is infected, provided that the official veterinarian has confirmed that the operations carried out there are such that the flocks are completely separate as regards housing, keeping and feeding, so that the virus cannot spread from one flock to another.