It only ran for one season (just 24 episodes). Maybe it just seemed longer?
It was good quality, and I like all of Gerry Andersons stuff, but he never seems to be given enough chances. Thunderbirds was cancelled - IMHO one of the biggest mistakes of all time! UFO was cancelled and replaced with Space 1999. I know Neo for one doesn't agree with me, but I think UFO was infinitely better.
I heard Gerry in an interview recently say that he was working on something new, with a new partner (he has separated from his wife, and former partner Sylvia Anderson) but he was being cryptic as to what it was. He was selling a few more old puppets so he must be short of cash (though his reason was that they took up too much room)