Airflow would be the main thing - you're back building a cold roof, and will need to ensure that there is sufficient flow through the soffit to the ridge vent.
Insulating the loft ceiling instead (which may attract a grant, iirc) would be less risky long term, as you're not messing with existing airflow function.
Thanks. The loft is already insulated, but will check if there are grants for replacing with better insulation.
Thr challenge is that I could feasibly do the loft roof in stages moving things around. Doing the same with the loft floor would be really challenging practicaly imo.
Airflow would be the main thing - you're back building a cold roof, and will need to ensure that there is sufficient flow through the soffit to the ridge vent.
Insulating the loft ceiling instead (which may attract a grant, iirc) would be less risky long term, as you're not messing with existing airflow function.