[zimpenfish]

I suspect that a black cab ceases to be a "black taxi" when it is no longer operated by a licensed black cab driver.

https://tfl.gov.uk/modes/driving/red-routes/rules-of-red-rou... specifically says "Licensed London Taxis" which I'm guessing Mr Fry isn't driving.

[gadders]

I suspect that the police/traffic cameras can't tell or don't check and that is how he is (or used to) get away with it.