From the British Pathe archive:
1946: Ashopton Village is submerged under the waters of Ladybower Reservoir. Shots of where the village stood, but no sound.
1947: Derwent Village emerges from under the waters of Ladybower Reservoir. Longer version without sound.
1949: Drought footage without sound, including Ladybower Reservoir. And a version with sound.
From the Yorkshire Film Archive
1959: Vixen Films -- The Empty Dams has footage of Ladybower, but not online. This does at least partly confirm the suspicion I had (backed up by The Times online archives that it was 1959, not 1955, when the village was visible again). I shall check Dad's reference books on Friday as well.
1996: A series of three films exploring Derwent Village and showing just how much is still there after over forty years. Part One. Part Two. Part Three.