Or rather, Quatermass ii. The whole series, from 1955, is on YouTube. The film quality isn’t brilliant, but it matches my (very young) childhood memory. The sound’s surprisingly good though; I’m assuming it’s been cleaned up.

It’s so bad, it’s actually quite good. Quatermass and the Pit next I think. It won’t take long to watch this series, since they’re only half hour episodes.

Before you consider viewing too, be warned that it’s unsuitable for children or those of a nervous disposition.