'Baby' is the fourth episode of Nigel Kneale's 1976 ITV series 'Beasts'. I also think it's the best.
When a young married couple move into an old cottage they are surprised to find a sealed pot in the chimney breast containing, well, no-one can really tell, not even the husband who is a vet. They both agree it's pretty horrible, though, especially the pregnant wife, who feels it is something unspeakably evil that must be destroyed.
Local yokels working on the cottage fill in the details: it's a witches familiar, a nasty creature conjured up by black magic - and it needs getting rid of, fast, before its owner comes to collect it...
The creepiest episode in the series, it does what Kneale does best: slowly and surely building tension and foreboding before providing a terrifying and chilling denouement. The first time I saw this I actually had to turn the light on before I went to bed. Luckily, when I did, there was nothing being suckled in the corner of the room.