The Stone Tapes (1972)

From the UK DVD packaging:

“Atmospheric seventies ghost story from the BBC. When scientists working for Ryan Electrics move into their new headquarters, a gothic mansion, they find one room unfinished. Strange noises are heard, and the builders are too frightened to complete their work. When the other scientists dismiss such fears as irrational whimsy, only psychically-minded Jill (Jane Asher) senses the dark secret that lurks beneath the building”

From my write-up posted on Letterboxd in 2014:

This interesting and well acted British telefilm has been on my radar for years and I’m glad I finally caught up with it. In many ways this low-budget production about paranormal investigators was way ahead of its time and it’s no wonder that it terrified home audiences in ’72. The use of sound was surprisingly smart and creative. Was particularly impressed with Jane Asher’s performance as Jill although I love watching her in anything.

The Stone Tapes makes a great double-bill with another infamous British telefilm about paranormal investigators, Ghost Watch (1992), which was banned by the BBC due its “reality TV” approach that scared the hell outta British TV viewers when it originally aired. Both films are available as a double DVD set in the UK if you happen to own a PAL disc player like myself.