Goldsmiths actually have both the Lloyd and MacColl/Seeger collections (or at any rate part of the latter; presumably the books as opposed to the papers). Bert's books are catalogued, but apparently his papers are not.

http://libweb.gold.ac.uk/collections/speccoll.php

It may be (and this turned out to be the case, I think, when similar rumours circulated about Kenneth Loveless' books) that the material that ended up with dealers was mostly review copies and the like, rather than part of the core collection. Do you have any more information on that?

Whether or not Dave will ever finish the biography remains to be seen...