Invasion is a modest, although never entirely a standout effort. However, it does touch on some of the atmosphere that some of its better American counterparts the likes of Invaders from Mars (1953), It Came from Outer Space (1953), Invasion of the Body Snatchers (1956) did. There is a fine opening in which director Alan Bridges lets everything take place amid the everyday a radar operator lazily reading a copy of G-String Tales; Edward Judds doctor dealing with a drunken nuisance patient; middle-aged Anthony Sharp driving home with a woman (Jean Lodge) who is not his wife when the alien steps out of the fog and is hit by his car. These scenes do a fine job in creating a sense of ordinariness among the various characters, something that the American alien invasion films never much concerned themselves with. Later Bridges builds a modest atmosphere of alienness out of the fog.
On the other hand, after a worthwhile set-up, nothing much happens. The story becomes slow moving and somewhat uneventful. There are various happenings around the hospital as they try to puzzle over the nature of the alien and then debate whether to believe his story, but this is mostly talk rather than atmosphere. Things are pumped up sporadically with the appearance of the forcefield and a scene where Lyndon Brocks car explodes as he tries to drive away, as well as Edward Judds venture down into the sewers.
The films major distinction of Invasion is that it builds on the same reversal of expectation about what at the outset appear to be sinisterly invading aliens that we had in It Came from Outer Space to create the first alien cops-and-robbers film. This is a theme that became popular in the late 80s/early 90s in the likes of The Hidden (1987), the tv mini-series Something is Out There (1988), Peacemaker (1990), Abraxas: Guardian of the Universe (1992) and Monolith (1994). Invasion is also commendable for adding a mix of ethnic (Asian) faces to the cast line-up, well before such became commonplace in US films.
Director Alan Bridges mostly worked in British tv and made several feature films, most famously the excellent Edwardian drama The Shooting Party (1986). His only other work in genre material was the original film version of the Stephen King novella Apt Pupil (1998), which ended up being shut down in mid-production before later being revived by Bryan Singer.