I have just returned from 3100 Massachusetts Avenue in leafy north-west Washington: the address of the British Embassy. The broad avenue, lined with diplomatic missions, snakes up a gradual hill from the city centre. You can be there any day of the week and there will be no one in sight, and only an occasional (diplomatic) vehicle sweeping past.
For the past 48 hours it has been the scene of a never-ending procession of slow-moving cars and pedestrians. Families, couples, groups of friends and individuals are making their personal pilgrimage to say farewell to Diana. Many carry flowers, some a small toy, others a card or a message.
There is a queue half a mile long to sign the book of condolences, but many ignore the formalities. They have their own ritual. A pause, head bowed, in front of an expanse of flowers and messages that resembles an ever-growing shrine; the tribute laid, another pause, a photograph taken for the family album.
This scene is being repeated across America, wherever Britain has a representation: in New York, Chicago, Houston and elsewhere. And as striking as the numbers of people arriving is the sort of people they are; not America's aristocracy- groupies, nor the celebrity-seeking "grannies". Nor are they predominantly expatriates, though there is a good sprinkling of them, too.
The only way to describe them is as "ordinary" people. Many are the young and young- middle-aged - the "Diana" generation. Couples have brought young children, groups of teenagers and students have come, not to sneer or to gawp, but to pay their respects.
There are gay and lesbian couples, demonstratively holding hands; visitors in wheelchairs or on crutches, and most extraordinary of all, in this very white part of Washington, is the proportion of blacks and Hispanics for whom upper Massachusetts Avenue is alien territory. There is anger as well as sadness in the air; one man made a bonfire at a Los Angeles newsstand of current editions of The Globe, a tabloid newspaper, in protest at the use of "stalkarrazzi" pictures.
In the United States, people have tried to explain the intensity of public emotion by saying that Diana, with her mixed-up life, her concern for her children, her eating disorders, her public divorce, her struggle to balance the private and the public and her resort to the confessional, was a figure Americans were able to relate to.
That may be the American explanation, but it is not the whole story. There have been similar public outpourings elsewhere in the world, and the complexion of the crowd appears similar. Outside the hospital in Paris where Diana died, there were more black and brown people than you would see in most Paris crowds. Whatever the truth of Diana's life and her personal misjudgements, whatever the privileges she was born to and married into, ordinary people abroad, as well as at home, felt she was on their side. Formal condolences from state leaders give barely a hint of the affection and regard in which the Princess was held.
This creates for Britain abroad a problem similar to the one that now faces the Royal Family at home. The monarchy has lost at a tragic stroke all that was young, beautiful, sympathetic, accessible and even relevant about royalty for Britons. That is also what Britain has lost in the world. For millions of people who knew or cared little for international diplomacy, Diana was the lively, modern and humane face of Britain.
She did not need the ambassadorship to which she aspired; thanks partly to television, partly to her own qualities, she was already a global ambassador on a scale that is only now apparent.
Her death may not impair Britain's formal diplomatic effort, but it will surely diminish Britain's international image and global reach. Even a young, presidential-style leader like Tony Blair will have a hard task to keep Britain in the same league.