After recently receiving a parking ticket we discovered that our car permit had expired the week before. Normally you receive an email from Wandsworth, but due to a computer glitch not all residents have received reminders.
Just in our road 3 residents have got parking tickets in the last few weeks, but understand one appealed his ticket on the basis they did not get a reminder and it was cancelled.
Worth checking the date of your permit and setting a reminder on your phone.