Is the contravention stated on the PCN correct as I only had the back wheels in the bay behind? A more appropriate contravention code would have been "Not parked correctly within the markings of a bay"?
Unfortunately not, because you have intruded into a bay with different restrictions. If you look at the photo of your car, you'll see the bay boundary, the double-dashed line between two separate bays. If instead of the electric charging bay, it had been double-yellow lines you would have been ticketed for being on them. So the PCN has been correctly served. Did you not check your car before you left it ? London councils make so much money from PCNs they can afford to flood the streets with CEO patrols, so it's always best to check one's car is parked OK before leaving it.