Can anyone give me a link to the youtube video of the guy who removed his TD5 headlining or a link to the guy who did it via pictures? Many thanks in advance.

Panic over. I removed my headlining this afternoon and found the problem. Seems as though Stratstone didnt fully seal the cups to the trim when they were both changed 2 yrs ago at a cost of £1600.
Did also do an experiment whilst we had the lining down where we put water into the surround and the vehicle was parked slightly uphill. Obviously the water drains away at the front but couldnt due to the incline. We noticed that there are several holes in the frame to gain access to the screws that hold the glass in place. Well lets just say that water was pouring through these. A bit of sniper tape on both sides of the holes cured that hopefully. So a top tip, always try to park with your nose pointing downhill if you are expecting rain!

Was here all the time!

https://www.landyzone.co.uk/land-rover/discovery-how-to-repair-a-leaking-sunroof-guide.171192/

Perhaps u should understand the design of the sunroof and why the drains are only placed at the front of each sunroof.
Water reaching the drain either means the sunroof is open, or what appears u have now a faulty seal.