(a)
Upon timely application, any person, who has an interest in the matter in litigation, or in the success of either of the parties, or an interest against both, may intervene in the action or proceeding. An intervention takes place when a third person is permitted to become a party to an action or proceeding between other persons, either by joining the plaintiff in claiming what is sought by the complaint, or by uniting with the defendant in resisting the claims of the plaintiff, or by demanding anything adversely to both the plaintiff and the defendant, and is made by complaint, setting forth the grounds upon which the intervention rests, filed by leave of the court and served upon the parties to the action or proceeding who have not appeared in the same manner as upon the commencement of an original action, and upon the attorneys of the parties who have appeared, or upon the party if he has appeared without an attorney, in the manner provided for service of summons or in the manner provided by Chapter 5 (commencing with Section 1010) Title 14 of Part 2. A party served with a complaint in intervention may within 30 days after service move, demur, or otherwise plead to the complaint in the same manner as to an original complaint.
(b)
If any provision of law confers an unconditional right to intervene or if the person seeking intervention claims an interest relating to the property to transaction which is the subject of the action and that person is so situated that the disposition of the action may as a practical matter impair or impede that person’s ability to protect that interest, unless that person’s interest is adequately represented by existing parties, the court shall, upon timely application, permit that person to intervene.