Although George Sanders and Maurice Evans have top billing before the title, Patrick Allen is the star and his name comes after the title. I like Allen's work, as in "The Long Haul" (1957) and "Tread Softly Stranger" (1958); and he does good work in "The Body Stealers" (1969) too. The ragged film editing (some awkward reactions shots) did George Sanders no favors, but neither did his part, which is quite empty. Maurice Evans comes off quite good; his part is far more interesting. Allan Cuthbertson plays a deputy minister, and he's excellent as usual. The two ladies are good too.
The movie's big drawback is the story and script. It's written by Michael St. Clair whose vita shows 32 acting credits. He tried writing twice, this one and another sci-fi movie called "Mission Mars (1968), done the year before. The continuity or story development or plot points do not build into something tense and interesting. Allen, for example, is conceived of as a skirt-chaser (as is Cuthbertson at times) to the point where the script wanders off into his affair with Lorna Wilde and his otherwise acute skills of mind seem to dissipate. Sanders and others have very little to do.
There is much better British sci-fi out there as fans know. This one is for completists only. "Quatermass 2" and "Quatermass and the Pit" are excellent contemporaries. Sanders has much better parts contending with "The Village of the Damned" (1960) and sequel "Children of the Damned" (1963).
Review by msroz from the Internet Movie Database.