Luckily the two Jaguar XJs's we mentioned previously had not yet been processed and we were able to retrieve the seat leather before the cars are crushed and recycled. One car was first registered in 1998, the other 1997, making them 18 and 19 years old respectively.
The majority of the leather is in fabulous condition, only the drivers seats showing wear (which we left behind). It would seem a combination of high quality material and low usage of passenger seats has meant the material has stood the test of time, and now will go on for a good few more years as a bag.
A bit of research on the web tells us that one car was last MOT'd in 2013, which means it could have been on the road up until its MOT expired in 2014. So it was still being used just a couple of years ago.
Looking around at all the lovely Walnut veneer adorning the vehicle interior when removing the leather material, it seems such a shame that we cannot yet harvest those materials too.