Across either end are heavy barriers, like those guarding an RAF base. These are operated by uniformed private security guards on 24-hour duty in sentry boxes.
But these measures were seen as so insecure that the Israeli embassy, next-but-one to the Kensington end, regularly took the precaution of having staff cars parked in the street outside, so no one could leave a car bomb.
Pedestrians and cyclists can use the street as a thoroughfare - cars cannot. But all a driver arriving at the barrier is normally asked is which number building he is visiting.
According to regular visitors, sometimes the guards will then take down the car number, and telephone ahead to the embassy to check the driver is expected, or even run a vehicle-driver check with the police national computer. But sometimes neither of these will be done and cars are waved through, or given only a perfunctory check. Taxis are always let through.
In these circumstances a woman in late middle-age, well-dressed and driving an Audi, might not attract much attention.
Sometimes, visitors say, the check with the police national computer can take so long that the driver has the chance to leave the vehicle before the answer comes back.
Outside each of the buildings, once grand Victorian mansions in their own grounds but now nearly all embassies, with a few owned by wealthy Middle Eastern families, individual security takes over.
Millionaire's Row, as it used to be called, always jealously guarded its privacy, but in the 1990s privacy has become high security. Many of the windows are barred with white steel mesh.
Video cameras bristle from almost every wall, panning passers-by. Most cars inside the secure area nestle behind high walls or gates. These carry diplomatic number plates and seldom leave. Some, from fallen Eastern European regimes, are covered in dust.
The Israeli embassy is guarded by Israeli personnel, with a member of Scotland Yard's Royalty and Diplomatic Protection Department stationed opposite. It is gated and walled against terrorists trying to storm the building, and may be reinforced as protection against a bomb.
Embassy security, and the security of resident and visiting VIPs, is the responsibility of the department. Its officers are trained in anti-terrorist techniques and can carry weapons, although they rely on counter-intelligence to anticipate any threat.
Two Middle East terrorist groups, Hamas and Hizbollah, have made several specific threats this year to attack Jewish and Israeli buildings around the world, and the Board of Deputies of British Jews has been liaising with the police.
Last week, following the Buenos Aires killings, the Board asked police to step up security on all Jewish premises, and Scotland Yard responded. But it refused a request to ban parking outside high-risk Jewish buildings. Since yesterday's bomb, parking at several specified sites has been banned.Reuse content