I am looking for the name of a tv series or movie in the 70s, feels very British, that had some human-like creatures (maybe smaller than normal humans) that had four arms.
The movie you're thinking of is called, "The Wild, Wild Planet," from 1965. It's actually kinda sick and messed up for a movie of that period. It's an Italian film. It was the first of a series of four films set on the Gamma 1 space station, that took place in the same universe. One of the movies was more-or-less remade as the infamous Japanese film, "The Green Slime."
Unfortunately, the description is still vague enough to cover a lot of ground. For example, I bet you could find alien monsters-of-the-week with three, four, or more arms in more than one episode of "Voyage to the Bottom of the Sea", "Lost in Space", "Space: 1999", at least one of the "Star Trek" shows, any of the 60 or 70 years of "Doctor Who" shows, and so on. The 1960s and 1970s saw a series of Mystery Science Theatre-worthy US/Italian/Japanese sci-fi coproduction films (including the infamous "Green Slime") that could fit the bill. The description might fit the 80s cult horror film "The Gate" (kids play a heavy metal record backwards, open a gate to hell, and unleash a horde of little gremlin-things led by a giant 4-armed monster). Multi-armed clay-mation nasties were standard fixtures the Harryhausen mythology films (Sinbad, Jason and the Argonauts, etc.) and elsewhere ("Equinox", for just one example). I think the Martians from the short-lived 1980s "War of the Worlds" television show might also fit.
Any chance of remembering anything special about the outfits the creatures wore, the things they did, the setting or plot, or anything like that, which might narrow things down a bit?