A tenancy, at will, is precarious. It can be brought to an end at the will of either party. The tenancy may be the subject of a written grant, but provided that it is for the best rent, reasonably obtainable and does not take effect as a term of more than three years, it does not have to be. The nature of the right granted depends primarily on the intention of the parties. Where parties are negotiating the terms of a proposed lease, and the prospective tenant is let into possession or permitted to remain in possession in advance of, and in anticipation of, terms being agreed, the fact that the parties have not yet agreed terms will be a factor to be taken into account in ascertaining their intention.