HOW TO EXPLAIN the success of "Upstairs, Downstairs," in 42 countries, with people as different as Americans, Australians, and Scandinavians? I tell my questioners the program is good, it's very good for a series. Not just the departments the audience is aware of, acting and writing, but camera work, set dressing, lighting, sound engineerings, etc. - hundreds of talented people, all working well together and with pride in the product, under two men, the producer, John Hawksworth, and the script-editor, Alfred Shaughnessy, who, because of background (upper or upper-middle class), talent and experience were the perfect men for the jobs.

This explanation is deemed insufficient, and my questioners supply the answer themselves with another question: "Does the class system still exist in England?" Yes it does, and so does the fascination it holds for people all over the world.

But to describe or analyze it is difficult because the rules or habits that separate class from class are unwritten. To climb out of your class in America is easy, that is if you find making money easy. In England, a man from the working class who makes a lot of money. A lot of money does not automatically give you a membership card to the middle class. Accent and manners (not necessarily good) are key factors.

To improve or change your voice with diction and elocution lessons is a help, but not enough. However beautifully you enunciate, your origins will condemn you, if, on being introduced, you say "pleased to meet you" instead of "how do you do." The use of words is very important: For instance, lavatory is posh, toilet is common. Lavatory is upper-middle, and toilet is lower-middle. Which word should you use? Do you adjust according to your company, or use a euphemism such as the john or the loo? If you are to the manner born, you won't question it; if you've learned it as I have and haven't enough confidence, you might prefer to wait until you get home where you know where it is and don't care what it's called.

I changed my class, temporarily, with a good marriage, but I was a reluctant, if not positively a bolshie, student. The rules seemed stupid, or "shstewpid" as I then pronounced it.

My husband one day asked me to transfer all of the articles in one beautifully tailored, but slightly shabby jacket to another beautifully tailored, but slight shabby jacket of a different color. You can wear suits or shirts as frayed and shabby as you like as long as they are made in Savile Row. He had three shiny fountain pens in his inner pocket. I put them, grandly showing their arrowed clips, in the breast pocket for all the world to see and admire. "My God girl," he said, "a gentleman never wears his pens on display." What a limited life a gentleman leads!

When I met him I though I had been very well brought up and had good table manners. After all, I never talked with my mouth full, didn't put my elbows on the table or dribble egg on my dress. Wrong! I committed two cardinal sins, I used my knife with the handle sticking out between my forefinger and thumb instead of holding it with the handle discreetly hidden in my palm, and horror of horrors, I thanked the maids or footmen serving the food.

Thanked them, you're not even supposed to look at them!I've solved the knife problem after years of practice, but I doubt I'll ever remember to ignore the maids. My mother now considers that I have atrocious table manners because I've mastered the art of eating almost everything, except soup and poached eggs, with my fingers. This in society is considered a little eccentric but perfectly acceptable, quite in the tradition of British individualism.

Why? Who cast there peculiar and humiliating, if you don't know them, laws? Well, nobody, they just evolved, it wasn't done deliberately with malice and forethought. All societies developed habits that set them apart, that identify them that create THEM and US. It seems to give a kind of security. The class structure in England is supported by all the classes, there is pride in knowing one's place, and I think this is partly what appeals to viewers in "Upstairs, Downstairs." The sense of order and unquestioned authority has disappeared, and people adrift in today's world hanker for a discipline imposed on them whether by God or man. The good old days? Not for me.

I am amused by exampled of class consciousness now. I can afford to be , for I can dine with dukes or dustmen, should I choose. I wouldn't want to be subjected to the limitations that were imposed on lower class young women in the golden age of Edward VII.

During the making of "Upstairs, Downstairs," I was made aware of how true it is still that all the English love a lord or lady. The cast worked like a repertory company, having equal opportunities. There were no stars, but the people working in the studio couldn't accept us as equals. On greeting the actors in the morning I was called Jean and invariably thumped on the back. The actress who played Lady Marjorie was greeted with "good morning, Miss Gurney" and a respectful distance was kept. She was also given the best dressing room even if she only had two lines. Advantages sometimes came my way as the public gradually accepted us as our characters - at a large London store I would frequently be sold foodstuffs at a cheaper price, the salesmen worrying about me, a maid, having sufficient money to buy salmon or filet steak.

I sometimes wonder if the "Upstairs" cast was making up this deficit when they went shopping.

Perhaps I've given the impression that the system is still as rigid as it was. It isn't quite. Society is a little more mobile, but the fact the phrases still exist, are used daily, indicates the system exists. Working class, lower-middle, middle, upper-middle, landed gentry, aristocracy, they all know their places still, but some question it. Aristocracy is only having your money for a long time. If you've had it long enough you can lose it and your social position will still be secure because you are at ease with those secrets of behavior that separate US from THEM.

Woe betide any newcomer who tries and fails to climb the ladder. Any gaucherie will be received with a lip curled in disdain - especially by somebody like me, a newcomer who succeeded. Of course it's easier for actors, we are tolerated as "artists" or court jesters. In fact, we've devised our class system, Upper Bohemia, Middle Bohemia and Lower Bohemia!

The success of "Upstairs, Downstairs" crosses all class barriers. It is watched by Masters and Servants, so I am persona grata both Upstairs and Down. And my old mum ain't 'alf pleased.