The show, which aired in 68 episodes from 1971 to 1975, followed the lives of the wealthy Bellamy family, as well as those of the staff who served them, in early 20th century London. It was originally conceived by actresses Eileen Atkins and Jean Marsh.
A 40th anniversary edition DVD collection of the series was recently released. It has more than 25 hours of never-before-seen features, including a five-part documentary called "The Making of Upstairs Downstairs," and vintage cast and crew interviews from Russell Harty's 1970s British talk show.
"Today, everything is so complicated, so fast," Down, who played Bellamy relation Georgina on "Upstairs Downstairs," told UPI in a recent phone interview.
"I think we have all this, that is immediate, instantaneous," she observed. "Someone dies, it's there on the news. You can see what's going on with horrendous things, such as [the earthquake and tsunami] in Japan, almost instantaneously, and I don't know that human beings are programmed to accept that kind of information, that quantity of information, especially that quantity of horror, every half hour. I think it makes people feel not important and helpless and, back then, when 'Upstairs Downstairs' was set, it was a time when life was much simpler. People were important. You could understand most of the things that were on the planet ... and that's what the show was about. It was about the people. Now, [dramatic TV] programs, for the most part, are about the story lines, murders, and things of that nature. They're not simple anymore. They're traumatic."
The 57-year-old actress, who also starred in the TV miniseries "North and South" and is now a cast member of the soap "The Bold and the Beautiful," said working on "Upstairs Downstairs" early in her career was an extraordinary experience.
"There are certain movies and shows that have been produced that really are not just perfect, but they are perfect in any particular time period," Down noted. "They don't age. It's not just the concept that Jean and Eileen had, but the people they were lucky enough to come into contact with, who then developed, produced, wrote and cast the show and continued in an unbelievable, 110 percent way to produce the show in such a way that everything was perfect. ... They were absolute sticklers for correct detail and even though it was a soap opera and it dealt with people's lives, it's a little bit like taking a skeleton -- which is what soap operas are like today -- and putting the meat and muscle and fat on the skeleton."
While historic events were often used as plot points on the show, Down said it was always the characters and how they acted in certain situations that kept viewers tuning in.
"Whether it was the house changing from gas to electric or the king coming to dinner ...," Down recalled. "There was an historic event or an event that was important to the day that was a trampoline for the episode and then all the characters would jump on the trampoline. It was like having an ice-cream sundae with double whipping cream and all the cherries on top, rather than just the plain ice cream."
Asked if she thinks the series influenced other works, such as the Oscar-winning film "Gosford Park" and TV's "Downton Abbey" -- both of which are also set in British mansions and follow the lives of the family and servants who live there -- Down replied: "I think it paved the way for all of those things. I think it gave the audience a hunger for things like that."
So, how does one move on professionally after working on a project as special as "Upstairs Downstairs?"
"I don't think you can top the notoriety of being involved in something like that," Down admitted. "Certainly, as far as acting is concerned, I've been better because I was very young."
A new version of "Upstairs Downstairs," with Marsh reprising her role of maid Rose serving a different aristocratic family in the same house at 165 Eaton Place, aired on PBS three Sunday nights this month.
Down said members of her fan club and people who follow her on Twitter initially told her they wouldn't watch the sequel because she's not in it.
"I tweeted back: 'Don't be stupid! Turn it on, enjoy yourselves!'" the actress said with a laugh.
Pressed to discuss whether she was approached to play Georgina again, Down exclaimed, "Oh, God, no!
"I think they quite sensibly made the decision that it would only be Jean, obviously, and then she got to have Eileen in it, who was supposed to be in the original, but she [couldn't be because she] was working. There was no reason to have any of the [other] original cast in [the new edition] because it was 40 years ago. So, I think it's not so much that they were going for the audience that liked the original, but something different, a new audience."