back when it 1st launched there talk of the possibility of free parking and what not if you had green plates to encourage adoption....... of course that has not happened - well not in my experience anyway....
I get free parking in Sheffield with a green permit, been using it for a year and just renewed it today for another year. Super handy to have, can park in any council managed carpark or side street within restrictions etc. Has made going into town so much easier if i need something instead of having to pay silly parking prices.