The McGuffin is on youtube

broadcast : Sunday January 12th, 1986

  https://www.youtube.com/watch?v=BoKyf4Eayiw#t=4208

 "Charles Dance plays a journalist who witnesses strange goings on in a flat opposite his rear window and from that all manner of spine chilling terrible events follow.its based on the novel by John Bowen"

late Roger Llyod Pack is in the cast
http://aboutactorcharlesdance.blogspot.fr/2014/01/roger-llyod-pack-and-charles-on-same-pic.html