Yeah, something similar in implementation. It actually seems like they already have systems like this in place, but they still only charge for access during congestion in specific zones. My suggestion is a bit different in that you would also be charged for non-congestion running time, outside of congestion zones.
Which, sadly, hasn't really done much to combat congestion or pollution. The only real solution is reducing the number of cars - unfortunately never going to happen in London.
No, the solution is to increase the charge until congestion is at the desired level. That's the whole point of charging for access: if you are supplying more than you'd like to, charge more until you're supplying just what you want.
If you only want a certain number of cars driving in the city with good reason, then charge the amount which gives you that number.
Perhaps the reason London hasn't set the prices correctly, is that they want maximum revenue instead of a truly limited supply.