This means that a vast number of tickets of dubious legality get issued. The best answer is not to ignore the ticket but to write or email an informal appeal to the ticket. If you email to firstname.lastname@example.org you will receive a reply from Barnet to say they have your appeal and so the time for paying at a discount will stand still i.e. you will still be able to pay at a discount if the appeal is rejected and you decide to pay.
From the Barnet Council website
If you challenge a PCN you should not make payment - on receipt of your challenge the penalty charge is frozen at the amount the charge is when your challenge is received.
We aim to respond to all correspondence within 10 working days, however this is not always possible so please bear with us.
With a little effort you almost certainly won't have to pay. The more people that appeal the busier it is going to get in the parking department and the more likely you are to win. Just think that you are contributing to employment by keeping the "information officers" ( a rather odd name for people who handle parking ticket appeals ) in a job.
So what should you write? This
I wish to appeal against this parking ticket numbered ******************* on 3 grounds under The Traffic Signs Regulations and General Directions 2002
1 the lines marking out the bay do not conform to diagram 1028.3 in that some of the lines are outside of the range of 600mm + 20% or -10%
2 there are not 2 signs of the type shown in diagram 663 at all entry points to the zone ( in particular there is only one sign, whereas there should be two, one on each side of Barnet Hill )
3 the signs on the poles do not conform to drawing 660.3
Please confirm that you have cancelled the PCN.
Check the signs for your zone - are there two at every entry point. If not, you should appeal.
If you have any problems please let me know. I will help you.