Woo hooo!
Finally found it this morning!
I was about to ring the passport office and find out how much it would cost to get a new one on super-pronto-delivery, but did some chores first.
It was....
In the laundry basket!
I have absoultely no idea how it ended up there. The only places the thing lives are in my jacket (which is leather, so gets professionally cleaned) my bag, or a file of important stuff. I don't even think I was wearing anything with big enough pockets I could have accidentally put it in there the day I lost it.
*shrug* found it now - and the house looks a lot tidier after the clean up / search
I am sooooo relieved!
Thanks for the support everyone