It's a new year, and apart from many other things that come with that (including 25 shiny new days holiday from work to use up), I have an added bonus - the six-month wait to see if my stony resolve won out has expired, and thus I have won the battle!
It is only a small financial victory - the opportunistic parking fine was cut down to £25 from £50 after I explained to them all the different reasons why they were wrong, but it was a matter of principle. And it's proof that if you receive one of these fines yourself, you can stand up for your rights and win. (so long as you have a good excuse anyway)
If you find yourself in a similar situation as me - a parking fine slapped on your windscreen when you return to your car - and you are in a privately owned car park (ie not a council one) then you have a good chance of also avoiding the fine.
1. Get photos of your car, the area and any signage.
2. Write a letter (using this as a template) explaining why it is wrong, including photos.
3. Resist the temptation to respond to any replies, unless they are official court orders or to do with the police (which if it is a private fining company, won't be if you have made a good case).
4. After six months from the ticket date, you can consider it abandoned.
The third one is the hardest. The parking fine companies will tailor their letters to look as threatening and as official as possible, whilst staying just to the right side of legal. You need to learn how to spot the difference between something with the law behind it, and a close facsimile just trying to scare you into paying. This website is a good place to check any received correspondence against letters received by others. Also Martin Lewis has his own section on parking fines and how to avoid paying them.
Good luck, and keep your nerve.