Yeah UFO the TV series was a big inspiration, can't say I was a fan of the show though, although you can easily tell it's a work of Gerry Anderson as the show is like Captain Scarlet except with humans instead of puppets
Being American, I never even heard of that show. Did watch Space 1999, which is, from what I read, the next season /generation/ whatever of UFO. Oddly, despite the extreme dated look, I did enjoy watching UFO.
Sort of fun, and I can see where things from the show were almost directly ported to XCOM. The GEOSCAPE, UFO detection, Interception launches, etc. Even there HQ is actually underground with a "front" organization (a movie studio!) at the ground level concealing the alien fighting organization known by acronym of S.H.A.D.O. SHADO counterstriking UFOs across the planet.
Its also clearly not a kids show, pointing directly to adults. Adultery, voyeurism, nudity...