The Knowledge of London is one of the hardest memorisation exams in the world, and it's the reason a black cab driver can hear "Savoy to a mews in W11" and start driving without a screen. If you've ever wondered why the test exists, what it actually covers, and how the drivers of pre-booked private hire — including ours — are licensed differently, this is the honest explainer.
What the Knowledge actually is
Administered by Transport for London, the Knowledge requires candidates to memorise roughly 320 routes — the "runs" of the Blue Book — covering the six-mile radius around Charing Cross: about 25,000 streets plus thousands of points of interest, from hospitals and hotels to theatres and blue-plaque houses. You've probably seen candidates studying: riders on scooters with a map board on the handlebars, "doing the runs" in every weather.
Candidates prove it in a series of one-on-one oral exams called appearances, where an examiner names two points and expects the shortest legal route, street by street, from memory. Pass everything and you earn a green badge — an All London licence to ply for hire anywhere in Greater London. The yellow badge is the suburban equivalent, covering a defined sector rather than the whole city.
How private hire licensing differs
Private hire drivers don't take the Knowledge — they're licensed by TfL through a different route built for a different trade. A TfL private hire driver holds an enhanced DBS check, passes a medical, completes a topographical skills assessment, and meets an English-language requirement — and can only work pre-booked jobs through a licensed operator in a licensed vehicle. The structural difference: black cabs can be hailed on the street and run a regulated meter; private hire is pre-booked, with the route planned and the price agreed before the journey starts.
Two systems, two pricing models
| Black cab (hackney carriage) | TfL private hire (fixed fare) | |
|---|---|---|
| Driver exam | The Knowledge (green/yellow badge) | DBS, medical, topographical assessment |
| How you get one | Hail on street, ranks, or app | Pre-booked only |
| Pricing | TfL-regulated meter — final fare varies with traffic and time | Agreed before travel — doesn't move with traffic, time or demand |
| Best at | Hail-now short hops in central London | Airport runs, pre-dawn pickups, groups, price certainty |
Neither system is "better" in the abstract — they're built for different jobs. The meter's strength is instant availability on the street; the fixed fare's strength is knowing the exact price of a Heathrow run before you leave the house. We worked the numbers in the black cab vs minicab airport showdown, and the practicalities of where each can actually stop in the terminus stations guide.
Related guides
Black Cab vs Minicab to the Airport
The 2026 statistical comparison.
ComparisonUber vs London Black Cab
Which is better, and when each wins.
DataDo Black Cabs Strike Too?
The 2026 data and what to use instead.
FAQs
How long does the Knowledge of London take?
Typically three to four years — roughly 320 Blue Book runs, around 25,000 streets and thousands of points of interest, proven in oral exams known as appearances.
What's the difference between a green badge and a yellow badge?
A green badge licenses an All London taxi driver to ply for hire anywhere in Greater London; a yellow badge is the suburban licence, covering a specific sector.
Do private hire drivers take the Knowledge?
No — it's specific to black cab licensing. TfL private hire drivers pass an enhanced DBS check, a medical, a topographical skills assessment and an English requirement, and work only pre-booked jobs through a licensed operator.
Does the Knowledge make black cabs more expensive?
Black cab fares follow TfL's regulated meter tariffs, which reflect the trade's costs and training. Private hire is pre-booked with the price agreed before travel — which is why fixed fares tend to win on airport runs and longer journeys. See the cost guide.
Know your fare before you travel
Pre-booked, TfL-licensed, and priced before the journey starts — no meter, no surge.