Thanks for your replies, much appreciated. Firstly, I do have a brewery, but my post about a drunk chicken wasn't supposed to be a wise crack, just the best description I could come up with. I do feed them on spent (beer) grains, but at that stage in the brewing process there is zero alcohol in the grains.
She has been like this for a 2 or 3 days, and hasn't been laying for about a week, it just seems as if she has no strength in her legs and they keep giving way. When hopping down from the coop this morning she just ended up on crumpled heap on the floor. I will read the links provided and search a little more and come back to you.
Thanks again everyone.