Mondeo Rear Seat Belts

I've seen a lot of posts asking for help when the rear centre seat belt on a Mondeo will not extract, so I am aware of the need for the
seat to be firmly locked before the belt will work.
However, I have a similar problem in that I folded the seats down to take some rubbish to the dump and now I can't fold the right one back upright as the belt will not release. I've tried fiddling with the seat locking mechanism but with no joy.
It looks like I'll have to cut the belt and get it replaced in time for my next MOT!
Is there a known cure for this?
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