My understanding is that there are no 'fair use' exceptions in British law. Someone like abigailb who knows more law than I do may be able to clarify this point.

Also, lending out the originals and having a photocopy backup does not solve the "two pianists, one piano part" problem with playing the work in two different ensembles.

Also, it should be public domain, damnit. The only reason it isn't is that either nobody has bothered to typeset it and put it into the public domain, or someone somewhere is sitting on the manuscript that would be a necessary source for such a thing.