When the sisters asked for the next rental payment, this had transpired and Cooper sought a declaration that he was the owner and that the lease was not enforceable.

Since Mr Cooper was the true beneficial owner, in equity, it was impossible for a lease to be granted to him in law.

It is stated by him in his Cause Petition, which is verified, and to which there is no contradiction, and in all probability it seems to be the truth, that his uncle told him, not intending to misrepresent anything, but being in fact in error, that he was entitled to this fishery as his own fee simple property; and the Appellant, his nephew, after his death acting on the belief of the truth of what his uncle had so told him, entered into the agreement in question.

I submit to your Lordships, therefore, that all that we can do is to remit the case to the Court of Chancery in Ireland, with declarations which shall enable the parties to have this question properly decided.Lord Westbury agreed, and expressed the issues as follows: The result, therefore, is, that at the time of the agreement for the lease which it is the object of this Petition to set aside, the parties dealt with one another under a mutual mistake as to their respective rights.

Private right of ownership is a matter of fact; it may be the result also of matter of law; but if parties contract under a mutual mistake[3] and misapprehension as to their relative and respective rights, the result is, that that agreement is liable to be set aside as having proceeded upon a common mistake.

But then, when the Appellant comes here to set aside the agreement, an obligation lies upon him so to constitute his suit as to enable a Court of Equity to deal with the whole of the subject-matter, and once for all to dispose of the rights and interests of the parties in the settlement.

And there is another particular also which must be noticed, which for the moment, I think, in the preparation of these minutes, has escaped our attention, namely, that unquestionably the Respondents were entitled to the cottage and to the piece of land, upon which no rent has been paid.

But, during the time that has elapsed, I understand the fact to be, that the Petitioner has had the possession and enjoyment of that cottage and of that piece of land.