15.—(1) An act done by a person in contemplation or furtherance of a trade dispute shall not be actionable in tort on the ground only—
(a)that it induces another person to break a contract or interferes or induces any other person to interfere with its performance; or
(b)that it consists in his threatening that a contract (whether one to which he is a party or not) will be broken or its performance interfered with, or that he will induce another person to break a contract or to interfere with its performance.
(2) An agreement or combination by two or more persons to do or procure the doing of any act in contemplation or furtherance of a trade dispute shall not be actionable in tort if the act is one which, if done without any such agreement or combination, would not be actionable in tort.
(3) This Article is subject to Articles 16 to 20.