Here we go chaps:
The Issue is caused by the outside seat lever not rotating the shaft enough that runs through the back of the seat connecting the inner and outer catches. So although the outer catch is released, the inner catch is not quite released enough to allow the seat to move.
So...
Firstly remove the seat lever by pulling firmly, and then remove the plastic trim panel, again a firm tug on the bottom edge and it comes off:
Next remove the screw circled:
Now you need to ease the metal bracket (circled in yellow) off the metal shaft (circled in red).
You will then see the shaft is splined. You now need to lift the seat lever on the other side of the seat a little so it rotates the link shaft teeth (circled red) anti clockwise 1-2 teeth. The metal bracket (circled yellow) it then pushed back onto the link shaft (now a few teeth offset from where it was) and the screw done back up.
Now when you lift the outer lever it should disengage both the outer and inner catch the same amount (the inner a little more than it did before) so they both release at the same time.
Hope this all makes sense, its a little tricky to explain!