Edwin Richfield, who plays Peterson, later went on to play the Minister in Hammer's third Quatermass film Five Million Years to Earth.
Brian Donlevy reprises his role as Professor Bernard Quatermass from The Quatermass Xperiment, making him the only actor to play the character on screen twice. In spite of this, he was reportedly "Quatermass" creator Nigel Kneale's least favourite actor in the role.
John Rae appears as the same character, "Mac" McLeod, in this film as he did in the original 1955 BBC TV version.
Hammer originally wanted their sequel to The Quatermass Xperiment to be the Jimmy Sangster-penned X: The Unknown, but Nigel Kneale vetoed the use of his character(s) by another writer, forcing script revisions on that film.
In between takes Brian Donlevy's toupee was accidentally blown off by the aeroplane engine wind machines used during the film's climax.
One of the first films (if not the very first film) ever to use the number 2 as an indicator that it was the sequel to another film. In a DVD commentary Francis Ford Coppola makes a similar claim for The Godfather: Part II. The Godfather Part II was released some 17 years after this movie.
The last surviving 35mm print of the U.S. theater version, under the title "Enemy From Space," held by United Artists, was reportedly cut up and used for land fill.
The ruined town of Winnerden Flats is at Ivinghoe Beacon (along The Ridgeway), near the village of Ivinghoe in Buckinghamshire, and is owned and protected by the National Trust.
The Shell Haven Refinery location used in the television serial was revisited for the film, which was able to make greater use of the location.
The telephone number of the Experimental Rocket Group is Camford 647.
Though recast, both Chief Inspector Lomax and Rocket Group staffmember Marsh return from The Quatermass Xperiment; neither had featured in the BBC version of this sequel. John Longden replaced Jack Warner as Lomax, and Bryan Forbes replaced Maurice Kaufmann as Marsh.