Right, done it!
The trim clips just need a long flat bladed screwdriver inserted above the black cloth bits to lever them out - alternating from side to side on each individual clip helps.
The hinge retaining nuts are 13mm and have to be loosened off a lot to gain any left/right wiggle room (actually by the time they're that loose the tailgate will move in any direction!). What I did was loosen them up a lot, then close the tailgate carefully with a wedge of paper on the left sill to help guide it across to the right a bit. Hop inside the car and (with back seat down!), tighten the nuts up a little bit, alternating from side to side until tight. Then outside and have a look, find the bottom of the gate was too low on one side, fiddle, repeat, fiddle, repeat... until I finally had it looking good and clearing the left sill. Possibly it may have been easier to do with the struts disconnected but possibly not.