They are the same material as modern bumpers so any decent body shop should be able to plastic weld it for you.

 

......... or maybe replace it?

LH Wheelarch Liner: P/N C2N2847
RH Wheelarch Liner: P/N C2N2847

I was surprised to find these are still available from Jaguar.

Graham

 

The ice that builds up under the fenders on the wheel liners cracked up my front liners very bad last year. I repaired then my taking them out and basically stitching them back together. I drilled matching holes either side of the crack and pulled it together with a tie wrap at each set of holes. Just pull hard enough to pull the joint together, then snip off the tie wrap and. I did this about every half inch. After I got the contours all correct I sprayed each side with spray flex seal, 3 coats and let it dry over night. It has held up well for over a year. Use the smallest size tie wraps you can find. I got black ones at the dollar store and then use a drill size that you can barely get the tie wrap through.