If you read a few posts as your roaming around the forum on this subject the good people advise that when one of the connector blocks in the passenger footwell gets damaged (usually through moisture getting into it) it is to blame for your interior lights not coming on when you unlock/open the door
Following ours stopping working shortly after purchasing our disco I thought I'd have a rife around,
Take the panels off the area where your feet go, there's two on ours a softish padded panel (under the glovebox) then the hard plastic panel on the side, it's held by plastic lugs, be careful & they come out lovely,
Then you'll see an array of wires & grey connector blocks, brown too. It can look daunting but your looking for one connector block & then one wire (blue & purple)
There's 3 blocks together, your after the middle one, to separate them they just slide off & on to each other, access is abit tricky but percevere. Once you have the middle grey connector block you can use a flat screwdriver or thin spoon handle to press the clip at the bottom middle to separate the block. (I personally don't like using anything with a 'sharp' edge when this close to wires) I depressed the tab then put spoon handle between block to separate by wiggling, then repeated that until they separated enough for me to just pull apart.
So now your blocks are apart if you look at the bottom corner wire/spade connector in the block it may be green? Yuck that's the moisture build up rendering the connector disconnected. From here there are a few paths you can go, as I used what I had to hand I'll go through what I did, using a pair of needle nose pliers or regular ones carefully pull one wire out of each side of the block, make sure it's the same coloured wire both sides (line up each side of the block if needed to visualise) it's the purple & blue wire. Pull out then carefully strip the sheathing off, about half an inch should do on both. Twist the copper so it makes a stronger end then using a white household connection terminal ( you can buy them in strips from most DIY stores) put each end in & screw down both screws to hold.
Done, well done. Put everything back together but leave the panels off for now, incase there's another reason to go in or so it's less to take if there's a problem. I shut the door locked it with the key fob & unlocked it started the engine (just to make sure lol) then locked it.
On unlocking it the lights came on woop woop, opened & closed the door, shortly after the lights dimmed & went out...job done well done peeps, hope this helps