Do I need to fir a threshold to the door frame between the garage and house

Surely the floor of the garage is at a level considerably lower than the bottom edge of the door and I would expect the door frame to already have a flush cill?   If you can identify the fire door to it's manufacturer or it's certification you will be able to find out the requirements for the threshold and Section 12.3 of BS 8214: 2016 Timber-based Fire Door assemblies - Code of Practice provides guidance about smoke sealing at the threshold.