Not trying to be snarky, given your user name, but am I safe we're talking about an Arnage that has this problem?
The "shredded" is secondary to being sodden, repeatedly, and drying out again, repeatedly. I had the same thing happen in my SY series car to one of the carpets.
I would not be shocked if you have a plugged AC drain tray drain. This was a problem for years with the "frog lips" one way valve at the bottom of the drain tube becoming clogged/sealed shut. Given how long Crewe often used similar technology, I would not be shocked if the same is on the end of your car's drain tube.
Even if not about your model specifically, it's worth looking at the following, as similar issues could be at play:
Tee-One Topics, Issue 90 "Keeping the Airways Clear" drain article for scuttle intake, page 1223, shows the "frog lip" valves in photographs. If you find something similar definitely check that it is not stuck shut.
There is an article in Tee-One Topics, Issue 12 (p. 137) that makes mention of wet carpet issues secondary to blocked drain hoses.
1) Is your a/c working and have you been using it recently? - Yes, probably the drain if it's been happening when you run your a/c
2) Do you park your car outside? - I expect that there are rain channels that can get blocked up by leaves , this happens to my Mercedes Benz S55 all the time and they need to be cleaned out