Sorry to hear about your parking ticket!
If the T's & C's state that if the machine(s) are not working you are not permitted to park, then you are stuffed (probably). If you have a witness , photo, or other evidence to support your claim that the one and only machine was not working , you should go for it! If you do not have witnesses ( known to you), you might want to ask the council for details of other persons so fined at or about the time you were fined, or you may have to threaten to pursue an order for 'discovery' of such information if the council refuses to give that information to you. Good luck, mate ! Richard
