Absence of reminders isn't usually considered good enough by the tribunal to allow appeals but it does depend on what system a council has set up. Here it doesn't seem there is anything to go on but the council should be reminded about their reminders.
What is something is that London Councils guidance is to issue a code 19 contravention for an expired permit and yours was expired by less than 2 weeks. Code 19 is lower level - £110 vs high level £160 - so it's a substantial difference and you can say they are demanding more than they should.
But this point could be made in the context of a polite ask for discretion - are you are long-term resident with a good record of paying permits and council tax on time.
At some point an expired permit becomes no permit - some councils have policies such as 1 or 2 weeks grace.
