Tim …
Dave Harker is indeed still alive and attended a meeting of the Traditional Song Forum when it met in Newcastle a year or two ago. He lives back up in the north-east again after many years in Manchester.
He has recently published a series of books on north-east singers and song writers:
Billy Purvis: The first professional Geordie
Cat-Gut Jim the Fiddler: Ned Corvan's Life & Songs
The Gallowgate Lad: Joe Wilson' Life and Songs

All three were reviewed in Folk Music Journal.

Derek