It's not just the thermal insulation considerations which are a problem.
This is a bathroom - warm, very moist air - so much moisture in it that it starts to condense even at the temperatures in the room.
You must, must, absolutely muststop that air from getting into the roof space, or you will get serious condensation up there and your roof timbers will start to rot.
You must be able to build or install completely sealed enclosures over the lights - no leaks in the enclosures themselves and no leaks between the enclosures and the roof side of the plasterboard.
My wholesaler sells LED down lighters which are only 12mm deep and are ideal for situations like this.
They are suitable for use in zone 1 and as they are not as thick as a standard ceiling board they can be installed without the need to remove any insulation above the ceiling.
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