The Owl Service was made into a TV series which I found in full on Youtube, although it is in separate parts. You can find the first episode (part 1) here: The Owl Service (right click to open in new tab)
It has an IMDB page here: The Owl Service (right click to open in new tab)
This is a description of its production provided by the Paul Harvey who posted the videos on Youtube:
The Owl Service was an eight-part television series based on the fantasy novel of the same name by Alan Garner. Produced in 1969 and televised over the winter of 1969-1970, the series was remarkably bold in terms of production. It was the first fully scripted colour production by Granada Television and was filmed almost entirely on location at a time when almost all TV drama was studio-bound. It used editing techniques such as jump cuts to create a sense of disorientation and also to suggest that two time periods overlapped. For the series, the book was adapted in seven scripts (later stretched to eight) by Garner and was produced and directed by Peter Plummer. The direction was quite radical and seemed to be influenced by the avant-garde, a noted contrast to what might be expected of a children’s serial. During a test screening of episode one prior to broadcast, the concern was raised that the story was difficult to follow, so recap sequences were added to the start of each episode which explained the story so far. On original broadcast, due to a technicians’ strike, the series was transmitted in black and white. Many contemporary reviews were complimentary about the production although some expressed the concern that it was not suitable for younger viewers. The Observer said that it was “far more than an ordinary children’s story” and made comment on “the adult passions working themselves out in the three adolescents”. The Sun commented that the serial would have the whole family “glued” for the next eight weeks, stating that it was “the most gripping, creepy serial we have seen on TV for a long time”. After the first episode was screened, the Daily Mail said that it had “all the makings of a first class horror story”. In 1970, ITV nominated the series for the Prix Jeunesse – the leading award for children’s films. The series failed to succeed as Plummer later explained: “the jury in Munich found it ‘deeply disturbing’ and questioned whether it was not indeed reprehensible to offer such material to young people”. Owing to this the series proved difficult to sell to overseas companies. During the 1980s however, many did purchase the series and was screened for the first time in countries such as Spain and Ireland. Still, some cuts were made to the episodes (such as Gwyn’s “Dirty-minded bitch” line and Alison’s scream in the final episode) although perhaps the most striking scene – a sequence from episode 3 depicting Gwyn’s struggle with Alison in what appears to be a simulation of rape – remained intact. Today, The Owl Service is considered by many to be a landmark in children’s drama and has been hailed as a classic production and daring in its presentation. The serial was repeated in 1978, for the first time in colour. This resulted in Granada placing an endcap with a copyright date of 1978 which might have confused viewers who didn’t realise it was actually produced nine years earlier. According to the TV Times, this repeat was a tribute to cameraman David Wood who had died a few months earlier. No reference was made to the murder of Michael Holden (who had been killed in an unprovoked pub attack the previous year). A further repeat took place on Channel 4 in 1987. Despite its success, The Owl Service was never issued on video, but was released on DVD in April 2008.