I also am plagued with the disease of hoarding. You are not alone Simon. Paperwork is my biggest downfall. I keep everything.
I did some thinking about it, and came to the conclusion that it validates my existence. I WAS HERE! or THERE! depending how long ago it was. I have utility bills from 30 years ago, are they antique yet? I also save nuts and bolts. It is very frustrating to know I have "One of those somewhere" but can't find it when I need it. I buy another and when I clean up I find 8 of them.
Last summer I was in purge mode and did very well getting rid of alot of junk. Plan to do the same this year. Wish me luck.