In reply to Indy:
I sent a big sleeping bag to mountaineering designs. It cost their fee and £10 in postage, but it has transformed the bag. It was away for about 2 weeks in total.
Shampoo on a sleeping bag isn't good - it will clean all the oil out of the down. Patch washing it might work, but I've only been successful washing a bag twice - once where I had access to a huge tumble drier and a top loading spin drier, and once where I had access to 'desert-grade sunshine' and a clean dustbin to wash it in. The tricky part is twofold - washing it in water and down cleaner without tearing any of the internal baffles, and secondly drying it, even with a tumble drier and spin drier.