Shackled together and released just in time for Halloween, these two classic BBC ghost stories have lost none of their power to jangle your nerves. Despite its reputation as a TV landmark, the notorious Ghostwatch was only ever shown once in the UK, on 31 October 1992. Such was the furore surrounding this unforgettable drama – about a TV investigation into poltergeist activity in suburbia – the BBC banned any repeats.

Although recorded weeks in advance and clearly publicised as a scripted drama, Ghostwatch was presented as a live on-air special fronted by a studiobound Michael Parkinson(playing himself very convincingly). The authentically rendered outside broadcast segments were handled by former Blue Peter presenter Sarah Greene and Red Dwarf star Craig Charles, who interviewed actors playing concerned locals and a family terrorised by a malevolent ghost.

The story was based on the infamous Enfield Poltergeist case of the late 1970s, in which a family in the London borough claimed to have heard knocking on their walls and seen furniture move. A children's toy was said to have been too hot to touch, and a photographer who visited the house claimed to have been hit on the forehead by a piece of flying lego.

Following a deliberately paced, innocuous start – the comforting presence of Parky and co is an inspired piece of misdirection – Ghostwatch gradually escalates into a terrifying ordeal, as the production falls victim to violent and disorientating poltergeist attacks. The sparingly used, almost subliminal background glimpses of the ghost itself – nicknamed Pipes, due to his banging and clanking – are a masterstroke, more unsettling than any amount of explicit horror. The makers of the 1999 shocker The Blair Witch Project were – by their own admission – taking notes.

Broadcast at a time when verité-style horror had yet to become commonplace, and echoing Orson Welles's 1938 War of the Worlds radio broadcast, Ghostwatch proved so convincing that the BBC received 30,000 calls from distraught and angry viewers. There were press reports of children suffering from post traumatic stress disorder – the involvement of Greene, a familiar face from children's TV, was singled out for particular criticism – as well as the tragic suicide of a teenager with learning difficulties, who believed his family home's faulty central heating system was caused by Pipes. Following a judicial review, the BBC was eventually cleared of all blame. Even today, when we can feel safe in the knowledge that it's all fiction, Ghostwatch is still an incredibly effective piece of experimental television. Just don't watch it alone.

Written by Nigel Kneale of Quatermass fame, The Stone Tape is another intense ghost story. First broadcast in 1972, and marrying science-fiction and the supernatural, it tells the story of a pioneering electronics company moving into its new research facility, a renovated Victorian mansion, only to discover that builders have refused to work in one particular room.

Empty apart from a child's letter to Santa ("What I want for Christmas is please go away"), it transpires that this room is haunted by the ghost of a servant girl. Rather than running for their lives, the boffins regard her as a scientific breakthrough: a mass of data ripe for analysis with their cutting-edge recording equipment. Naturally, their interference proves rather unwise.

Aided by the atmospheric direction of Hammer veteran Peter Sasdy, and by an extraordinary soundtrack from the BBC's legendary Radiophonic Workshop (a gurgling soup of growls, scratches and harrowing screams), Kneale's typically intelligent rumination on technology versus the unknown is an unforgiving assault on the senses, and quite possibly the noisiest drama ever broadcast by the BBC – with the exception of anything starring Brian Blessed.