It won't be enough for your friend to merely show that he was not driving the car on that day; he has to prove that he was not the registered keeper. Firstly, has your friend checked with DVLA that their records have now been updated and your friend has been removed as the owner of the vehicle? If so, this should be all the evidence you need. If not, your friend needs to provide all the evidence he can that he did not own the car at the time of the incident. Did he take a photocopy of the log book showing the new owner's details before he sent it off? If he can demonstrate movement of money into an account (i.e. payment he received for the vehicle), this could help. Has he tried to contact the new owner to see if they will provide a signed statement (nothing fancy, just a letter will do) to the effect that they are the owner (I know they will be landing themselves in it, but they may do the decent thing). Finally, if the congestion peeps do pursue with a county court claim, your friend could, in turn, claim against the purchaser of the vehicle, though I personally wouldn't recommend this as it is more hassle than it's worth, especially for such a small sum.