The serial sees Professor Bernard Quatermass of the British Experimental Rocket Group being asked to examine strange meteorite showers.

[4] This was less than a month before the shooting of the location filming for Quatermass II began, and necessitated the casting of a replacement lead actor at short notice; John Robinson was chosen to fill the part.

[5] Robinson was an experienced actor from a range of different films and television programmes since the 1930s,[6] but was uncomfortable about taking over from Tate, and had difficulty in learning some of the technical dialogue he was required to deliver.

[5] As Hugh Griffith also had problems with some of his technical dialogue, Grey learned his lines as well as her own, in case she needed to step in and assist him during the live performance.

Roger Delgado, who found fame in the 1970s as the Master in Doctor Who (1971–73), played a journalist who helps Quatermass before falling victim to "the mark" in episode four.

[14] and Melvyn Hayes, who played the small role of Frankie, later worked in several films with Cliff Richard and starred in the BBC sitcom "It Ain't Half Hot Mum".

[17] Kneale credited the director Rudolph Cartier with bringing to the screen in Quatermass II, with its ambitious location filming, an expansive style that had not been seen in British television drama beforehand.

After a farmer finds one of the objects in a field, the soldiers become directly involved, and Captain Johnny Dillon decides to unofficially ask the father of his fiancée, Paula, to investigate.

After the guards' departure Quatermass speaks with a tramp, who explains that there used to be a small government research unit consisting of a few huts by Winnerden Flats, and that a year ago they expanded and bulldozed the village, and built the plant and a prefab town for the construction workers.

Back at the Rocket Group, Leo and Paula deduce and discover with a radio telescope that an asteroid is orbiting the Earth invisibly and discharging the meteorites when it reaches the near point, 400 000 miles over Southern England every 14 hours.

Quatermass deduces that an alien life-form which comes from one of the moons of Saturn, which lives on ammonia, hydrogen and methane, but to which oxygen is a deadly poison, travels to earth in the meteorites, and in the few seconds they spend out of their shells before dying they possess human minds, and transmit knowledge to each other in a collective consciousness.

Quatermass is narrowly saved from discovery by the rioting construction workers, who storm the plant and along with him are besieged inside the gas distribution centre, where they pump oxygen into the completed pressure dome to poison the ammonids, however some of the workers succumb to propaganda from the plant controllers, who offer them the chance to see inside the dome.

In anger, the remaining workers fire on the dome with a bazooka, igniting the hydrogen and subsequently destroying the entire plant, killing the ammonids and releasing ammonia gas into the surrounding area.

On 22 September 1955 the ITV network was launched in the UK, bringing commercial television to Britain for the first time and ending the BBC's broadcasting monopoly in the country.

[22] Having recently signed a two-year extension to his BBC staff writer's contract,[23] Nigel Kneale was specifically commissioned to write a sequel to The Quatermass Experiment in early 1955 to challenge the new ITV network.

[18] Since the first Quatermass serial, the two men had collaborated on the literary adaptations Wuthering Heights (1953) and Nineteen Eighty-Four (1954), and on Kneale's abominable snowman play The Creature (1955).

[28] Most of the pre-filmed material was shot on location at the Shell Haven oil refinery in Stanford-le-Hope, doubling for the factory where the alien creature is being grown on Earth.

[28] Filming also took place in rural Essex for material showing the meteorites being discovered in fields, and in the boiler rooms of the under-construction BBC Television Centre in London for scenes set inside the factory.

[32] A BBC audience research report commissioned after Quatermass II had finished found that 90% of those questioned in the sample had watched at least five episodes of the production.

After some debate as to whether the letter was a journalistic trick to uncover advance story details, Kneale eventually decided that it was genuine, and allowed Cartier to send a reply outlining the storyline's conclusion.

[1] Writing in The Times in 2006, Morgan Falconer claimed to find racist undertones in the serial: "Quatermass, for instance, often seemed to have an unhealthy preoccupation with blackness, a barely veiled commentary on racial change in Britain.

[35] However, this interpretation of the serial is not widespread, and is undermined in episode five where an Irish immigrant helps Quatermass sabotage the aliens' food supply system.