10 rules to driving a black cab

Yeah but seriously, isn't it illegal to drive with only your parking lights on, it makes em harder to see.
Highway code rule 113: You MUST use headlights at night, except on a road which has lit street lighting. These roads are generally restricted to a speed limit of 30 mph (48 km/h) unless otherwise specified.

So sidelights are fine, in fact much better. If all cars only used sidelights they would drive more slowly and carefully. Cyclists and pedestrians would stand out more instead of everyone being blinded by bright lights. So the cabbies, and me, who use sidelights only should be encouraged.

Most people drove around London using only sidelights before 1974.