Only way I can think of to get out of it is check if there are any mistakes with the markings. There's a huge volume of silly little details that have to be right for markings to be enforceable, and if one tiny detail is wrong, the fine and points will be invalid.
I can understand why they punished you though - an obstructive car could cost a life if it blocked an ambulance, and though that wasn't going to happen in this instance they have to be consistent, same rule for everyone. People are far less likely to do the same thing again if they've been fined rather than merely had a telling off.
I do think it's too harsh though - I'd say just a fine the first time and dish out points to re-offenders.
Incidentally, I got a £60 fine for parking on a yellow (I usually only go there off peak, completely forgot it was rush hour) and only had to pay £30 because I paid promptly. For thirty quid at least you could get drunk a couple of times.