What is the test for a defendant to successfully defend a claim for trespass on another person's land?

If the entry is admitted or proved, the defendant to successfully defend the action must show that he was justified in so doing. This he may do by showing that he entered by the leave or licence of the person in possession, or that the entry was made in the exercise of a legal right. This legal right he would establish if he showed that his entry was made in conformity with some recognized principle of the common law or the provision of some statute. The common law recognized the right of a person to enter upon the land of another under certain circumstances; for example, where it was an involuntary or inevitable accident happening without negligence, or to escape some pressing danger or apprehended peril, or in the execution of legal process or lawful distress, or to abate a nuisance on the land entered. The right was also recognized where the entry was reasonably necessary for the preservation of the property of the person entering, or of the person whose land was entered. But to justify the entry on this latter ground it had to be shown that the danger to the property was grave and imminent, not a mere straying of cattle on another’s land (Cope v. Sharpe [No. 2] [1912] 1 K.B. 496, 81 L.J.K.B. 346; 27 Halsbury, 861).