Kia Sportage seatbelt

[ColinM50]

Centre seatbelt, which is hardly ever used has somehow got trapped and the webbing is torn almost completely through right at the top where it disappears into the roof.

Firstly I can't see how to get the casing off to fix it. Is it just a lever under job? And secondly if I cut it off is that MoT failure?

TIA