Dai, I've been scouring Waterstone's (bookshop) as the library is shut. Alba is consistently derived from a shrunken form of Albion ie, the part free of the English (or the Romans before them?). (I was joking about the chalk.) I have seen one reference to a tripartite division into Cambria (I'm chickening out, sorry), Lloegr and Alba based on a Welsh Triad, which pushed it back pre-Roman, and linked Lloegr with the people of the Loire region in France. However, this book was definitely one of those discovering ancient secrets things, so not respectable as an academic reference.