In leases it is not uncommon to make provision for periodic reviews of the rent and to impose on a lessor, who wishes to take advantage of such a provision, the necessity of his initiating, or ‘triggering’, the review by a notice served on the lessee at or before a certain date or within a certain period. In this article, we respectfully submit the House of Lords to have mistaken the nature of such impositions; and that it is because, and only because, of that mistake that the House has held such time limits to be, in the absence of the grossest indications to the contrary, merely ‘directory’ and so freely to be disregarded by lessors.