Thing to remember here is that it might be like in France, where the points can still end up on your licence. So could end up on your wifes friends licence.
Its a fixed penalty, no points...and i aint married, thats my ex who came to visit cos im smashing!
Just write back saying that the vehicle is right hand drive, so as the photo doesn't show the driver you can't be sure who was driving it as various members of the family, mates, friends, kids, best mates pet budgie, all have access to the vehicle at any time and you don't keep records. If they can supply a photo of the driver you might be better able to help, otherwise ....
I dont give money to the government without a fight, it eats into my booze and bird budget.
Write them a letter saying how they have cause distress to your wife as they have sent a photograph of your mistress to your house by error as your car is right hand drive so she was not driving. Under their privacy laws which they have blatently ignored you would like compensation please
Next time wear a ski-mask, or a burka.
No law against that.
CharlesY