And in my experience, Mumbai's taxis almost never run by a meter, and when they do it's very obviously rigged (at least when used by pasty Scots).

Ah yes you were charged the white tax. Mumbai taxis are actually famous for going by the meter while pretty much taxis in other metro Indian cities dont.

Since you dont look "Indian" the taxis know they can get more money out of you.

Next time before you enter the taxi try saying "Meter say chalo" which in Hindi means go by the meter.

Yes, I/we were charged this tax on more or less every rick/taxi ride.

If I even asked for the meter (in English, mind), rather than negotiated a price beforehand, we invariably got a rigged meter anyway! I'll try it in Hindi if I ever get back though!