I'd like to see more, and better quality, photos. I agree it looks like some sort of cloth, or could it just be the normal trim covered in a fine growth of mould
I don't think cloth was ever a listed option on the P5/P5B, although some destined for Govt use were trimmed in cloth by Hoopers, but they were saloons. That doesn't mean the original owner didn't have it retrimmed. I've seen cloth trimmed Rolls Royces, yet always thought half of the appeal of the RR/Bentley was the leather interior.
My first impressions are not that of an 'obsessively maintained' 36,000 mile car.
I'm also not sure about the colour, it looks like Zircon Blue / Silver Birch (roof) to me, which was a P5B colour, but not a P5 one. P5 coupe colours for 1966 were Steel Blue/Charcoal (roof), Light Navy / Steel Blue (roof), and for 1967 model year Admiralty Blue/ Silver Birch (roof). Also, P5s didn't have the coachline.
According to DVLA it was regd. end of July 1966, so should be a '66 model.
Of course, there are many 46 year old cars that have been resprayed and retrimmed, but at a genuine 36,000 miles? I know some owners might have treid to update their P5s when the P5B was announced, but the usual obvious way was with Rostyles, which this one doesn't have.
Still, yet another Mk111 P5, of which there aren't many about now.