P38A Headliner issue

For the first time since we bought this p38 it rained, and the headlining got damp on the sliding cover for the sunroof. Now the headlining came off the plywood sort of material and I cant glue it properly back on. This is a problem because now it wont open without using a screwdriver to push the fabric along with the sliding cover.

My question is, do I need to drop the whole headliner off to get good access to it or how do I fix it?

Yes remove the composit shell clean off any crumbly foam and re-glue headlining on with spray adhesive...it's a pain of a job as you have to remove A,B, and C piller plastic covers...

There's a how to in tech section top of main range rover page

Here is Dopey`s how too guide

^^^^Good guide.

It's the foam backing on the material that's the issue.
Deteriorates over time with heat & just ends up as a crumbly mess even though the material is still fine.
It all needs to be scraped off the backing board & if you're trying to refix the old covering it all needs to be cleaned off that as well.
High temp resistant adhesive required.
The Martrim one is instant grab with NO scope for repositioning whatsoever so best to have a helper to hold the material up as you smooth it into position.
Avoid stretching the material as you put it on, as it will try & shrink back & pull the foam away.

Thank you all for the replies, but what I am trying to fix is the trap door thing at the sunroof. The liner there came off and the material seems to be some sort of plywood. The question was if I have take off the whole ceiling to work on it.

It's plastic or should be. I've heard of it being possible to bend it and prise out but I'm doubtful.
Yes, headliner out complete to fix, I would take it out anyway and have a good look at the foam strip between the sunroof tray and the underside of the roof, you can't see it very well until the headliner is out. This strip is vital as it acts as a water shedder and directs water that does get past the glass seal into the sunroof cassette tray and down the 4 drain tubes instead of onto the headliner and water in the cabin. I glued a new foam strip on after cleaning off the old and am now leak free. 2 metres of 20mm x 10mm closed cell strip and some bostik. Sunroof cassette is very heavy, 2 man job unless you're built like a brick outhouse which I am not anymore.