Kevin - The relevant measurement is the track width, not the car's overall width. If the car is parked close to the kerb, and at least part of the offside wheel is on the white line, then it should not get a PCN.
Chris - It looks to me, having tweaked your photo so that you can actually see where your nearside wheel is relative to the kerb (see below), that you didn't park particularly near the kerb, probably about 25 cm away from it. If you insist on having such a wide vehicle in London, then I suggest you take more care with your parking.
You say that "even with our neighbour's M class parked opposite there is plenty of room for trucks etc to get through without slowing down." I beg to differ. I think you'll find that your road is 8 metres wide. If two of you have M-class Mercedes parked 25 cm from the kerb, then even with wing mirrors folded, the two of you would be taking up 4.32 m of road space, leaving just 3.68 m for traffic. The minimum width for emergency vehicles recommended by fire brigade is 3.7 m.
