People here complain endlessly about the National Health Service, which is financed by taxpayers and provides access to care, free at the point of delivery, to everyone in the country. They deplore the system’s waiting lists, its regional disparities in treatment, its infection-breeding hospitals and its top-heavy bureaucracy.

But they can be a bit touchy when outsiders are the critics.

They are furious, for example, that the health service is being held up as an example of the failures of socialized medicine by Americans opposed to President Obama’s health care proposals. On Wednesday, several dozen people rallied in front of the American Embassy in Grosvenor Square, holding up pro-N.H.S. signs.