Thank you, Newt. I guess it has to be a Project UFO episode. I saw this many years ago on Australian TV, and only came across Project UFO when it was screened on Australian Foxtel pay tv in the 90's. I thought that it might not be Project UFO as the episodes I saw on Foxtel didn't match the 'feel' that I remembered from my childhood. But now I see that it was right at the end of the second season, which might explain the difference in feel.
Thank you for helping me solve a childhood mystery! I loved that show as a kid.