That is a very good question!
The title caught my eye, as I have always believed that the Engineers who designed the F INTENDED that there should be proper wheel arch liners in the rear arches, as well as the fronts.

In the case of the nearside (or LHS to be clear for our European friends who drive on the wrong side of the road!) the brake hydraulics would be receiving some protection.  The junction visible in my photo is (apparently) notorious for corroding.  Keeping dirt, mud and salt-laden water at this time-of-year seems like a good idea to me.  The two holes and the step highlighted with green circles in my photo below look as if they were intended to allow a wheel-arch liner to be attached.  Why would Rover pay Stadco to do the extra tooling and pressing operations for these features UNLESS they were intended for this purpose.

Has anyone made a suitable liner?  Can a liner from any other vehicle be adapted for our cars?
Any insights would be VERY welcome.