The only reason CPZs exist is because as soon as one council implements a zone, motorists get "squeezed" to areas either side of that zone. The local councils in the UK have adopted a "divide and conquer" method to parking zones, where they restrict parking in one area, which makes like intolerable for people who live in adjoining "free" areas. Those free areas soon have to become controlled parking zones too.
So, just scrap every single parking zone in the UK and we will all be back to square one, plenty of parking spaces that are free!
Oh sorry, I forgot the flaw in the plan. Without parking revenue, our local councillors wont receive gold plated salaries and pensions.