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Well, that's just a kind of road user charging. In this instance, I think it would be quite regressive and at any rate there'd be plenty of drivers in this area who could easily afford it. Also, ANPR is really not the future of road user charging. It's a technology that has been available and reliable for some time, and there's a general hiatus while people are trying to work out which system (of many possibilities) to go for, but eventually it'll look very different from the rather cumbersome and infrastructure-heavy stuff we have now. It'll probably remain in certain locations, e.g. around the City, but it's not going to be implemented in Richmond Park.
I think the best suggestion I saw was ANPR which would charge you a fee for exiting at any gate other than the one you came in.