Has anyone else got broken or damaged extensions to the rear wheel arch liner? The nearside has broken off completely, which I suspect was done when driving over a farmer's field to the car boot car park. It has exposed the seam and cill. I suppose the only remedy is a replacement liner or just forget it!

Perhaps coat it heavily with underseal if you don't want to buy a new liner?

I may treat myself to a new liner. The driver side is fractured but not sheered off. I avoid bumping up high kerbs which may have damaged both sides. I suppose the flexibility in the plastic has reduced over the 10 years and the liners have become brittle. Over the 10 years of ownership this has been the only problem incurred. 

Yes may be a sound move especially if you decide to keep the car long term.