There is also Zipcar Flex in London. You can park the cars in on-street parking, even paid or residents bays. But they have only agreed it with some councils so far. Map: https://www.zipcar.co.uk/takethebluepin#zipzone-map

I would how risky that is for Zipcar. What incentive would there be for the council to say no to a competitor offering more money for the spaces?

uk gov might not work like a greed corporation as its usa counterparts. usually when a deal is stabilished with one company, others can jump in for the same price/share. the worst that would happen for zip car is to have to share the spaces.