Yep, the “Complete Method for the Harp” is by David Watkins, published by Boosey and Hawkes,1972! Although if it is in reprint it may be a different publisher. I suspect you may be able to get it from Holywell…
What does it cover? It starts assuming a complete beginner and has excerises on scales, arpeggios, chords etc. It includes advice on tuning and sitting at the instrument. And interestingly has photos of both flat and curved fingers on the strings.
It includes his suite of Six Pieces – Prelude, Bercuese, Gigue, The Nightingales, Dance and Nocturne. For beginners and playable on lever harp.
Later in the book he also includes his Second Suite for harp – March, Blues Waltz, Nocturne and Rondo.