(1) Where, in the case of any action for which a period of limitation is fixed by this Act, the action is for relief from the consequences of mistake, the period of limitation shall not begin to run until the plaintiff has discovered the mistake or could with reasonable diligence have discovered it.

(2) Nothing in subsection (1) of this section shall enable any action to be brought to recover, or enforce any charge against, or set aside any transaction affecting, any property which has been purchased for valuable consideration, subsequently to the transaction in which the mistake was made, by a person who did not know or have reason to believe that the mistake was made.