My ancestor Mary Ann Harper is frustratingly elusive as mentioned here. However, Harper is a surname that would lend itself to different spellings in censuses, birth records and the like — Harper, Harpur, Harpe are just a few that come to mind — and that's before I factor in possible mis-transcriptions when searching indexed sources online.
Is there a (preferably online or currently in print) reference that would identify all the possible alternatives for a given surname, including likely mis-transcriptions? I'm particularly interested in English and Welsh surnames. I'm aware of First Name Variants By Alan Bardsley that links different variants used for forenames but no printed equivalent for surnames. I've also looked at Thesaurus of British Surnames and the sites that page links to, but that doesn't seem to deal with mis-transcriptions.