SophieHatter

Thanks for all the answers so far!

RE time - yes, I agree my plan was to see how it goes and give them the front half with a note that I'll need it back to attach the rest of it if the back isn't ready!
RE wool - I've just dug out the baby quilt I inherited from my great uncle from the cupboard, which is indeed very nice, but quite heavy. It appears to be a) made of wool and b) not eaten. However, something seems to have destroyed some of the patches in a strange way (which is why I can see the batting). I think it may be unwashed wool - it's kind of yellow - with the lanolin still protecting it, and I'm not sure that's very good for the cotton! I agree that wool is good, but probably not worth the risk - a housefull of moths would not be a good wedding present.
Re polyester: I've also now investigated the other quilts I made: one is at Gran's house, and I always use it on my bed when I am there, and Gran uses it on her chair. It is very cuddly, and the middle is made of polyester. I found the offcuts in the attic here, and it seems to be lovely soft fluffy polyester, and very different from the strange stiff crackly polyester that the other two quilts I made is stuffed with. Of those, one was in a drawer in the spare room because it was so much stiffer and harder to wash than a blanket, and the other Mum has taken the middle out of because she didn't like it. So now I can see what makes for good polyester! I agree that it can meet the criteria, but only if I get the right sort rather than whatever is to hand.
RE Warm and Plush - I've also heared lots of good reviews about Warm and Natural, and was wondering whether to use that - is it similar?
RE wholecloth blankets - that's an excellent idea, what's the best sort to use? Is it flannel as in towelling, or thinner than that? Is it what we call "waffle" in the UK? Flannel as in brushed cotton seems too thin! Presumably I'd have to find one the right size, or it would unravel if I cut it? Or I could give up on environmentally friendly and use a polyester fleece blanket, which doesn't unravel. I was also wondering if I might do something similar and cheat a bit and get some of that batting that has hideous backing cloth already thoroughly quilted to one side, and then quilt the back through both sides of that and cover the "backing" with the front? Might get a bit too much of a sandwich, though!