However, linger a while and the real Harley Street can be deciphered. Consultants who work there say that it is no longer the preserve of the medical elite; it is now home to the 'best and the worst'.
Surgeons who have touched royalty murmur 'Good morning' to 'doctors' who have never been to medical school. Consultants who pay up to pounds 20,000 to rent a suite live next to NHS rejects who choose to 'squat' and run a 'private practice' to earn a living.
Asked to estimate how many of his 2,000 colleagues in Harley Street might be 'bogus', one gynaecologist said: 'up to one in 10'.
How can the public distinguish the rotten apples? You can't, was the reply.
The street where once the principal landlord, Lord Howard de Walden, could be choosy about the tenants and still count on making pounds 6m a year, is sprouting To Let signs.
Doctors wanting to set up a practice used to be carefully vetted. Not now. 'Anyone can claim to be a Harley Street consultant if they have a bit of money and a business card,' said Dr Percy Thompson Hancock, 90, a retired oncologist who worked there for 40 years.
In the past, doctors shared their practices for years. They knew each other intimately and would refer to each other as one-ers, two-ers or three-ers depending on their income. All that has gone. The turnover is so high that checks or discreet enquries are impossible.
Alasdair Fraser, a Harley Street consultant obstetrician and gynaecologist, says that the brass plates at the doors are a good indication of how 'reputable' a consultancy might be. Some doctors whiz in and out so quickly that they don't even bother slotting their names into the brass frames by the side of the door.
Among the chief offenders are slimming therapists, psychotherapists, women's services, hair-replacement surgeons and cosmetic surgeons. Two months ago a Harley Street hair-replacement therapist was found guilty of defrauding bald clients. But not one of the doctors I asked about the incident appeared to have heard of him.
Of greater concern are the well-established Harley Street 'specialists' who have been found guilty of misdemeanours. One even hired an assassin to murder a colleague. Then there was the surgeon who was struck off for taking part in the sale of kidneys. Last year yet another surgeon was erased from the medical register when he carried out an illegal female circumcision.
But Dr Thomas Courtney is the most infamous of the Harley Street rotten apples. He was sentenced to seven years' imprisonment in December 1992 for raping and otherwise sexually assaulting patients.
Courtney's respectable image was almost impossible for the public to penetrate. He had set up a string of charities (how was the public to know that they yielded nothing after donations totalling pounds 400,000?); he had rubbed shoulders with Cabinet ministers and Downing Street advisers.
But members of his profession knew that he was a charlatan, a bluffer. Several doctors expressed concern to the General Medical Council about his qualifications and psychological fitness, only to be met with a deaf ear, according to Martin Page, the author of a controversial book, The Good Doctor Guide, now in its second edition.
Anywhere else in Europe, or in the United States, Courtney would have been investigated and convicted for quackery at the outset, says Page.
But under the GMC's aegis, the protection of patients in Britain lags half a century behind the rest of the Western world.
To illustrate the extent of the problem, Page carried out a survey on a sample of 250 doctors practising in Harley Street. He found that more than a quarter were not accredited or qualified in any specialism.
But, under the General Medical Council rules, they are all able to call themselves 'specialists'.
The GMC seems to think its procedures are quite adequate. When asked to explain what 'serious negligence' is and what would be done about it, a spokesman took great delight in reading out long passages from the rule book.
What it boiled down to was this: if the doctor is a registered doctor, the GMC can do something about it. If the doctor is not, the GMC has no authority. In the last recorded year, 1,301 complaints were submitted to the council. Out of these, only four were considered 'serious' enough to merit striking the doctor off the medical register.
The areas most open to exploitation are weight problems and 'women's problems', according to Alasdair Fraser. 'It is quite easy to set up in Harley Street,' he said. 'The landlords don't check a person's qualifications.
'Once students have been awarded a degree they can call themselves anything. They can describe themselves as 'competent' or they can describe themselves as a 'specialist'. Who is to know?
'Some of the doctors in Harley Street do not have a medical degree. Others have, but they've not been successful at medical school.
'You get people going into private practice because they have not been very successul climbing up the NHS ladder.'
Even those who have been struck off the medical register can continue practising. According to the GMC, a person who has been struck off can continue practising as a consultant as long as he does not write a prescription.
Mr Fraser has some advice for patients seeking 'specialist' treatment: get a referral from your GP or go to your local library and check how much training the 'specialist' has really had.
Varied experience in the NHS is a reliable guideline.
Alternatively, you could try nearby Wimpole Street. It is now the hot tip if you want the cream of Britain's medical profession.