Section 51.

1. A construction affixed to a relevant property (whether on or below the ground) and used for the containment of a substance or for the transmission of a substance or electric current, including any such construction designed or used primarily for storage or containment (whether or not the purpose of such containment is to allow a natural or chemical process to take place), but excluding any such construction used solely to induce a process of change in the substance contained or transmitted (in paragraph 2 referred to as the ‘substance concerned’).

2. For the purposes of paragraph 1 the following shall not be regarded as a construction used solely to induce a process of change in the substance concerned, namely any individual item of plant used or primarily used -

(a) for containment or transmission, or

(b) for one or more actions or a series of actions,

that may take place, before or after, the occurrence of action that induces, in a separate construction affixed to the property, a process of change in the substance concerned.