On the one hand, as a cyclist/train commuter I'm very much in favour of this, but I appreciate that's because there's no cost to me supporting this.
On the other hand, I worry about ending up with a situation like Bristol. People are livid with the council there over the ULEZ. My parents visited recently and got over £200 in fines they never knew existed.
I think the main point is that the implementation needs to be correct. Any charges should be reasonable, predictable, and easily avoidable through a healthy supply of alternative transport links. Cities like Cambridge could provide a template for reducing congestion in similarly sized towns across the country, so it's important that they get this right.