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The crawl spaces are built as cold roof meaning they are designed for air to enter the space, if you insulate along the tiles then you will trap moisture, you only insulate at rafter/tile if the space is a warm roof meaning there is no airflow and it’s part of the heated space.
As long as the stud walls and the loft floor are insulated to regulations then that’s enough just ask building control if they have inspected and approved these elements.
It’s likely then you have alot of moisture rising up into the loft room from the house below. Heating will help but definitely get the extractor working in the bathroom up there and open the window vents and this should balance it all out.
The extractors and trickle vents work together to move air around the house, vents bring fresh air in when extractors come on and pull air out. Without both you get stale air sitting in rooms which can add to moisture. Turn the heating on for an hour then switch the extractor on for abit and you will get the moisture out whilst it’s not in use up there