A century ago, they negotiated treaties, entertained monarchs, debriefed spies and rallied the morale of isolated compatriots in dusty corners of the world. An ambassador's role today seems much reduced. He, or increasingly she, is on hand to greet a junior minister, arrange a conference call, address a business seminar and grace a diplomatic reception, mixing canapés, clichés and shop. Her Britannic Majesty's once plume-helmeted symbol of authority has turned hotelier, PR official and patron of the expatriate amateur dramatics society. Cynics suggested some years ago that he should be replaced with a fax.

The diplomatic uniform, crisp telegram, ballroom chandeliers and air of suave condescension have long been swept away. But embassies still have a real job to do: honing policy, projecting their country, spotting talent, trends and revolutionaries, and arguing a tough case on the chat shows. Britain tends to conduct its bilateral policies through its embassies overseas, which makes London a prestigious but often frustrating posting. The US ambassador's job, in particular, is more social than crucial. But a good envoy can still make a difference. Robert Tuttle, who leaves next month, has worked hard to draw the venom of anti-Americanism, bolster myriad links and offer a smiling welcome to the 25,000 visitors to his Regent's Park residence.

In general, the shabbier the residence and tougher the conditions, the more significant the role of the ambassador. Kabul makes the point. As a rule, the more luxurious the embassy furnishings and the larger the grounds, the less the work done. The heads of government in Rome, Paris, London and Washington talk to each other already by video conference, or, failing that, through their chiefs of staff. The ambassadors are, if they are lucky, patched in on the call.