20. An authorised officer may, by notice in writing served on the owner of an animal or batch of animals, require him to detain the animal or batch of animals at the place where it then is, or to remove it to such other place as is specified in the notice and detain it there, to enable the animal or batch of animals to be inspected by an authorised officer for the purpose of ascertaining whether there is present in it an unauthorised substance or a residue of an authorised substance which an authorised officer reasonably suspects may result in any product derived from that animal or batch of animals containing an authorised substance at a concentration exceeding the relevant maximum residue limit or whether or not any withdrawal period has expired.