Thanks to my friend Brett for his advice about washing/treating (down) sleeping bags. I have now used Nikwax’s Down Wash & Down Proof products http://meaningoflite.com (sent from England in 1 litre containers via eBay – cheaper than 300ml avail locally: 150ml of each needed per sleeping bag) on my ‘worst’ Montbell Ultralight Super Stretch Down Hugger #3 bag. During the drying cycle I stopped every few minutes after some drying had occurred to separate out the clumps of down. Gradually I teased them out until I had achieved pretty much the loft of a new bag (if not better).
I think next time I will try six tennis balls in the drier (they come in packs of three). They really do the job! I am really pleased with the result. I had substantially ruined this bag by having it saturated during a flood (twice) and having to sleep in it in any case. Then leaving it neglected for a couple of years. I will now try the products out on a bag which is mainly just dirty, and has not been allowed to re-loft enough.
Nikwax also have excellent products for waterproofing (eg leather) shoes/boots.