It's a corrupt industry that deserves to die

It's not corrupt. It's a straight up mob, that moans about their "rights".

This is good to know for London specifically.

It's not as satisfying as yours but my general technique that works everywhere in the world where cabs are competing is: ask them if they take credit cards and their reader is working before you get into the cab. If they say no you find another cab. (In my experience they never say no anyway. But I learned to do this every single time I use a cab anywhere because this scam is so unbelievably common everywhere in the world.)

My general technique is to use Uber, or pre-book a cab from the office. I have to admit I was stuck last time I was in Beijing, and of course nobody* takes cash in Beijing.

Yep indeed, I've asked before I got in. In this case I was getting a cab from the airport after a long haul flight. I'd normally use Uber but to try and speed things up I took a black cab because they're allowed use bus lanes and it was 9am.

Yeah as the other poster said, asking before getting in the cab is the other solution. Honestly the hassle of knowing it can happen, or wondering if yhe driver is going to be an ass about it makes it not worthwhile when I can tap a button and have an Uber appear for the same price, and _knoe_ my payment method (amex, to make things worse) will be accepted.