Remove the plate at the rear first, then slide the cover to the rear. Some clips may still break, but you don't need them all, three or four will hold it on satisfactorily. Vx probably still stock them, if you can find a dealer still open at this troubled time.
Ignore the above. All wrong...
Turn the steering wheel fully to the side you are working on.
Remove the torx screw from under the front of the sill cover.
Pop off the black plastic clips from the bottom edge of the sill cover.
Slide the sill cover forwards until it falls off. (you may need to pull the bottom edge down slightly to clear the clip pins).
Push the centres in on the two rivets on the rear plate and retrieve from under the car.
Pull the rear sill plate off.
Refitting is not the reverse.
Relocate the sill cover in position (line it up with the front wheel arch) and slap it onto the clips with the flat of your hand.
Refit the plastic rings underneath along with the torx screw.
Refit the rear cover followed by the two rivets.