This is a fondly remembered sci-fi horror film that appeared regularly on British network TV in the 1980s. It wasn't the first adaptation of John Lymington's novel and was first made as an ITV teleplay in 1960 which has long been forgotten. One can't help believing that ITV produced the adaptation as opposition to the BBC's QUATERMASS serials and on the surface there is something of a QUATERMASS vibe to NIGHT OF THE BIG HEAT. There is a major stylistic difference from the works of Nigel Kneale and this film and that is Nigel Kneale is an astonishingly clever and subtle writer where as NIGHT OF THE BIG HEAT while being enjoyable as entertainment is incredibly dumb
The major problem with the horror genre - and the reason it's held in low regard by critics - is that in order for the plot to progress logic and continuity must be ignored totally. Think for example how many times you watch a vampire movie the heroes wait until after sun set before deciding to enter the vampire's lair to kill the bad guy. Here we see a similar type of stupidity. Suppose you were being menaced by an alien creature that moves at a speed of a snail what would you do? Run away or stand around waiting to be burned to death or barricade yourself in to a stone shedcave with no means to escape and wait to be killed? Guess what the characters in this film do?
Having never read the original source novel I looked up wikipedia to find that in Lymington's book the alien monsters are giant carnivorous spiders which would make for effective and dangerous monsters than the ones seen here which resemble giant fried eggs yolks. It should be remembered that in 1967 there was no way a film company could make convincing giant spiders on screen but even so the aliens do look totally ridiculous when they finally appear at the end of the movie. And again the lack of internal logic and continuity means they remain unseen by everyone except their victims and manage to appear in a room with closed doors and disappear without being spotted after they've killed someone in said room with closed doors. The solution to the alien invasion is also a major cop out
That said it's certainly an enjoyable film for an unquestioning unthinking audience. I certainly have a soft spot for this type of dumb SF horror movie which the British film industry sometimes produces. It's not a Hammer production but has Peter Cushing playing an affable gentleman and Chritopher Lee as an abrasive scientist and features familiar British actors seen in film and television from the period.
Review by Theo Robertson from the Internet Movie Database.