The mind truly boggles. Either you are a complete moron or you are trolling. Probably you are American and you expect everyone to know where every road is because back home they are all numbered.
Go look at the A-Z of London, and then ask yourself "If I memorized the entire lot, how long would it take me and how much would I expect to earn per hour for driving people around".
> It seems the Knowledge only extends to main roads beyond the North Circular and this individual had to resort to his A to Z to find the place.
Go look at what the knowledge is: http://www.the-london-taxi.com/london_taxi_knowledge
It's about ROUTES from one area to another - ie how to get around london, not about memorizing the entire map of london. It is also about MAJOR landmarks (Embassies, restaurants, hotels etc) not some poxy B&B in a back street.
> If you are a visitor who doesn't know the area, you are not going to be much help, are you? Which is why you engage a supposed professional guide
Did he get you there?
Presumably he got you from the airport to the general area by memory alone, then had to look up exactly where the side street was.