Thought i'd just make a quick guide on how to do this as when I looked there was nothing. Pretty simple to do but just incase anyone needs it:
First thing is to remove the black cap for the back seat release, you need to place a screw driver under it to prise it off.
Next prise out the light with a flat head screwdriver. (on left side only)
And remove the connecter from the back of it.
Now remove the 2 torx screws holding on the parcel shelf support (T16). And pull the shelf support up and towards you and after a bit of jiggling it should come free.Be careful of the boot light switch, be sure to disconnect that too.

Now lift up the rear bench and undo the bottom of the seat belt. (17mm)
Next prise of the black cap at the top of the seat belt and undo the bolt holding it on. (17mm)

Make sure you tie a not in the belt at this point so the belt doesn't retract the whole way in. And finally release the last bolt holding on the seat belt mechanism. (17mm)

Now re do those steps and replace the seat belt, the only trouble I had was putting the parcel shelf supports back on, I found that you have to place a flathead screwdriver down the hole that the seat release switch goes through and push it towards you so it alines and slots in.
Once your done you should end up with some nice new seat belts
First thing is to remove the black cap for the back seat release, you need to place a screw driver under it to prise it off.

Next prise out the light with a flat head screwdriver. (on left side only)

And remove the connecter from the back of it.

Now remove the 2 torx screws holding on the parcel shelf support (T16). And pull the shelf support up and towards you and after a bit of jiggling it should come free.Be careful of the boot light switch, be sure to disconnect that too.

Now lift up the rear bench and undo the bottom of the seat belt. (17mm)

Next prise of the black cap at the top of the seat belt and undo the bolt holding it on. (17mm)

Make sure you tie a not in the belt at this point so the belt doesn't retract the whole way in. And finally release the last bolt holding on the seat belt mechanism. (17mm)

Now re do those steps and replace the seat belt, the only trouble I had was putting the parcel shelf supports back on, I found that you have to place a flathead screwdriver down the hole that the seat release switch goes through and push it towards you so it alines and slots in.

Once your done you should end up with some nice new seat belts
