OK. I removed the two plastic plugs on either side of the hand grip at the bottom of the door. Then, taking my life in my hands, I pulled the door liner away from the door. Misplaced confidence combined with brute force. Loud sound of cracking plastic.
Only to find that the hatch door has double-skinned metal in a number of places, making it imposible to hammer out the dent from the inside.
To replace door lining you line it up carefully and push it back into the metal. It is fixed by a number of plastic plugs which push in. Unfortunately some of them will break in the process. All very flimsy.
Now I have a door with a dent and barely attached door lining.