BMW 320 estate rear seatbelt fix

The problem is that the seatbelt on the backrest of the wider section of the folding rear seat retracts as the seat back is folded, the inertia reel mechanism won't then release the belt to allow the seat to be raised again.
On the parts diagrams, there seems to be some sort of cable which presumably is intended to disable the locking mechanism when the seat is lowered? It doesn't work! The car has been back to the dealer with this issue & apparently it's not uncommon.

The seat back has to be removed & the end of the belt removed from the body as the belt will ONLY pull out if the seat back is at the angle it would be in its raised position.

This is how to do it:
Remove left wheel arch trim, it is removed from the top first, you might like to loosen the plastic trip at the top first (two screws by the load space cover bracket) but we managed to get it out without. It unhooked from the bottom as you lean it forward.
You can now see the hinge fixing bolt, remove it (large torx socket)
It is now possible to remove the left side seat back by working it towards the front & left of the car, it is not easy, the pin in the centre of the car stays in the right hand seat back & is about 3" long.
The left seat back is now free but tethered by the other end of the seatbelt, you won't be able to pull it out yet as you can't get the seat back upright. You now need to get to the other end of the belt which is bolted to the body below the rear seat base.
Remove the right side wheel arch trim, hinge bolt & seatback (just as difficult as the left one!)
Remove the boot floor trim/carpet & lift the back edge of the seat base, it will move just enough to get access to the seatbelt bolt.
The left part of the seatback will now come out, you can hold it at its normal operating angle & pull the belt out!
Pull it out & tie a knot loosely in the belt to prevent it winding itself back in.
Put it all back together, as the Haynes book used to say "reassembly is the reverse of dismantling" !
Never ever fold the left seat back down again! (Maybe fit some sort of clip, something like the sort of clip used to seal plastic bags in the freezer? If you do need to?)