There has been numerous MOT failures here in the UK,the centre seat belt that is inside the fold down seat back is prone to failure,it usually jams solid and is unusable.There are various options,depending on how much you wish to spend to fix it:-Main dealer prices would be expensive,as the seat has to be dismantled,(removing the foam interior etc.,)& this would incur high labour charges.If you are prepared to do the work your self you could install a replacement into the existing seat back,I find the easiest and cheapest is to get a complette one from the breaker's yard,there is lots of them and you should be able to match the colour ok.However,that's the easy part,there is a "key"inserted into the anchor housing which must be disconected,the attachment shows how to do this.It seems to be a "secret"as the dealers don't want you to know about it.Also do not condem the belt until you have made sure that the seat has been "slammed" shut,it is this catch that releases the belt.Good luck!

i had this problem with my 2000 Mondeo.

I tried banging it back and hitting it with no luck.

Make sure the belt is disconnected from the buckle at the bottom to give you more play

The middle seat belt mechanism has a wire connecting to the seat lock which keeps it upright (this is to keep the the belt locked when the seats are reclined forward), if you peel a bit of the fabric seal away around this you will see the wire, it's easy to do but looks tricky.

I disconnected the seat lock (2 * star bolts)and kept flicking it on and off, not sure by luck or good judgement but it came free, once i'd put it all back together and slammed the seat back,

worth a try only need the one size star bolt

Hope it helps