Always appeal. There are so many loopholes for getting off, eg: the Parking Attendant (PA) has to stand on the pavement in front of the car to write the ticket; the PA has to sign and date the ticket correctly; some boroughs insist that the ticket has to be placed on the vehicle to be valid or it's considered a 'ghost ticket'. There are many more. Wort a punt, unless you're blatantly taking the piss by parking on double yellows, in a bus lane/red route or in front of a dropped kerb.