//Uber drivers don't need the knowledge - they have GPS devices in their cars which has calculated the most efficient route before they've even picked the customer up.//
I agree up to a point, Jim. And that point is Central London. SatNavs are all well and good in most situations. In Central London they very often simply don't work. They don't take account of temporary road closures, ceremonial events, regular congestion, demonstrations and so on. Black cab drivers do.
That said, don't get me wrong - I hold no brief for Black Cab drivers. They are extremely expensive and drivers can - despite the conditions of their licence - be very inflexible if the journey does not suit them. I don't often use a cab in central London. I know my way around very well on foot and by all methods of public transport and generally don't need a cab. But on the rare occasions that I do, it will be a Black Cab for me. But when I'm out in "the sticks" (which for me is roughly outside the North/South circulars) Uber works fine as do many of the conventional PH cab companies that I use.