The definition of an ambassador has undergone a subtle change. Discreet diplomats can expect scant attention as long

as photographers have access to the slinky Myleene Klass in India as an “honorary ambassador” for London. David Beckham, whose addiction to endorsement is as pathological as it is profitable, does not just advertise mobile phones; he is their “brand ambassador”. And now taxi drivers are being wooed with long-haul freebies in return for becoming rolling ambassadors for distant cities' tourist boards. The logic is impeccable. Word-of-mouth marketing is priceless, and cabbies have more words per mouth than anyone. It started in Melbourne, has now reached Bangkok and there's no telling where it will end.

“Going down the docks, are you? You seen the boats down there, huge they are. Cruise ships. Lovely time of year for it. I reckon that's how heart attacks happen, when people don't get away. You want to go on holiday, mate, treat yourself. Funny enough, I got some brochures here, Caribbean, the Med. Help yourself.”

The high street can't be immune. “Where to, love? Topshop? Ooh, dunno about that. I had that Sienna Miller in the back last week. Dropped her off at Miss Selfridge, that's where they're all going.” Nor should the NHS miss out on viral marketing. “You two got a kebab back there? Shocking for cholesterol. Had a few, have you? D'you know booze kills 8,000 people a year? Am I dropping you two off together? Well, if you can't be good, be careful.” Whisper it kindly to Becks and Myleene, but in the brave new diplomacy they're already looking old.