Once a Jimny has larger wheels fitted it is normal to cut back the flares on the wheel arches to prevent them rubbing. This means that the factory fitted wheel arch liners no longer fit and in my case they have been thrown away at some point in the past.
This then leaves a large open gap in the rear of the wing through to the door hinge. When off-roading this then fills with mud and is impossible to clean. Worse still is that even when cleaned it still seems to bleed mud out down the side of your car and in my case, with a black coloured car, it looks permanently dirty.
SteveW has sent in the solution below. He has cut soft plastic to shape and inserted it into the wheel arches. It certainly looks neat and is therefore high on my own list of things to do - look out for my version in the future.
Many thanks to Steve for sending this in.