“(c) if he damaged or threatened to damage the property in question or, in the case of an offence under section 4, intended to use or cause or permit the use of something to damage it, in order to protect himself or another or property belonging to himself or another or a right or interest in property which was or which he believed to be vested in himself or another and the act or acts alleged to constitute the offence were reasonable in the circumstances as he believed them to be.”.