ID an adaptation of The Little Mermaid with dark scary atmosphere

Question

Trying to track down a live action version of The Little Mermaid I saw as a child.

• I watched in the UK in the late 70's or early 80's.
• Very possibly it was dubbed into english but I can't be absolutely certain.
• seem to recall watching it on TV so there is a chance it was TV drama as opposed to a feature film but cannot be certain.
• atmosphere was quite dark and otherworldly and seem to remember scenes with objects moving backward as if the film was reversed.
• I recall one detail that frightened me a lot as a child. The mermaid character leaving bloody footprints as she walked. This scene may have taken place in a long corridor but I cannot be certain. My sister recalls this scene taking place on a beach so clearly our recollections are not too accurate.

Answer 1

The bloody footprints detail immediately reminded me of the Czechoslovak version of "The Little Mermaid", Malá Morská Víla. I do not know if it was shown on British TV, but the film was released in 1976, so it is certainly consistent with the dates in the question.

To confirm my (possibly faulty) memory, one of the reviewers on IMDB explicitly mentions:

When i saw this movie in 1977 on the TV i was impressed and touched by it. Remember crying at the end of the movie. It was very touching. The way the father appears at the beginning on the rocks. And the way the mermaid leaves the bloody footprints on the sand at the beach.

The full film can be seen on YouTube. The bloody footprints are visible at 1:04:45.