Regardless of the ceiling construction details, cold roofs installed with vapour permeable (LR) underlays and high level ventilation will meet the requirements of BS 5250: 2002 amd 1.
BS 5250: 2002 amd 1 describes alternatives to this solution and all eight alternative solutions can be found by following the link above.
A 'well-sealed' ceiling contributes to the airtightness of the building and provides a more energy efficient solution.
Guidance on the airtightness of ceilings can be found by following the link above.