I'm not convinced that ULEZ is going to be the vote winner that Susan Hall thinks. What was most unpopular about it was the fact that some people had to scrap their cars, but that hit is more or less over and done with and, even for those people, reversing ULEZ won't help them. A hefty proportion of the population doesn't drive anyway, and the majority of the rest already have ULEZ exempt cars - and quite like cleaner air.
I've also noticed that there seems to be greater compliance with the 20 limits. For some time I found myself with impatient queues behind me if I kept to that limit, but now more and more people are just driving at 20 habitually and the queues aren't happening nearly so much.