Your house is an end terrace with a larger garden, both of which are usually considered more valuable features. How much more is the question to be sorted between you and your landlord
If you get to 16 May and nothing has happened you just continue to occupy on a periodic tenancy.
Indeed I have found an end terrace with slightly larger garden because is around 10% more than a mid terrace with smaller garden. Especially as end terrace has direct garden entrance without going down a little walkway or similar for things like pulling bins out etc.
So a house around this was is £900 mid terrace and around £975-£1000 end terrace. I would say the difference between £725 and £855 is a little high since the previous difference was £30, however I could easily see that being £800-£810 tbh.