This was 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 (1974), which was released 17 years after this film.
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.
Brian Donlevy reprises his role as Professor Bernard Quatermass from The Quatermass Xperiment (1955), 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.
In between takes Brian Donlevy's toupee was accidentally blown off by the aeroplane engine wind machines used during the film's climax.
At no point during either of the Hammer/Donlevy Quatermass films is the central character referred to as a professor.
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.
This would be the last Hammer sequel to use a number in the title until The Woman in Black 2: Angel of Death (2014)
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.
Edwin Richfield, who plays Peterson, later went on to play the Minister in Hammer's third Quatermass film Quatermass and the Pit (1967).
Hammer originally wanted their sequel to The Quatermass Xperiment (1955) to be the Jimmy Sangster-penned X the Unknown (1956), but Nigel Kneale vetoed the use of his character(s) by another writer, forcing script revisions on that film.
Originally shot in AnsaColor, developed by Agfa, but released in Black and White. The colour negative still exists in the archives.
John Rae (McLeod) is the only actor to reprise his role from the original television version Quatermass II (1955)
Though recast, both Chief Inspector Lomax and Rocket Group staff member Marsh return from The Quatermass Xperiment (1955); neither had featured in the BBC version of Quatermass II (1955). John Longden replaced Jack Warner as Lomax, and Bryan Forbes replaced Maurice Kaufmann as Marsh.
The telephone number of the Experimental Rocket Group is Camford 647.
Quatermass drives a Mark 6 Humber Hawk estate car, registration SRW 745.
Michael Ripper (Ernie) later played a sergeant in Quatermass and the Pit (1958).