The annual rent is £13,704 before any costs, so there is not much room for several assumptions to be mildly wrong. I would pay particular attention to tenant turnover: an empty period, marketing, cleaning and repairs can arrive together rather than neatly across the year. Model financing...
There is a middle path: explain that the market evidence suggests a larger gap, but propose a smaller figure in exchange for stability. Put the new amount and date clearly in writing, and avoid presenting an asking-rent comparison as a threat. Before doing anything formal, confirm which increase...