His procedure was, put bluntly, to collect every name of a person named Sankey that he could find, then draw connection lines between them. The result is not only fantasy, but gets the known major families wrong as well. It must be read with this warning foremost in mind.
This is a scan of a photocopy of a photocopy of this publication. It has been annotated by several hands along the way.
A copy in the Bodleian Library, with different annotations, is online at Google books.
My carefully researched ancestry is here.
It's remarkable enough that no fantasy is needed!