Why do I have to pay from my tenancy start date when I don't move in until later?

You need to start paying utilities for the property as soon as you become responsible for the property, which is your tenancy start date.

The tenancy start date is the date you and other housemates become responsible for the property and for the utilities at this property, even if you aren’t moving in straight away. You are usually always liable from the start date of your tenancy agreement.