You got sent the fine because you were still registered as the owner, but as you already filled in the paperwork you wouldn't be liable.
This case will never stand up simply because of the appropriate documents being filed.
“Because he chose to buy my motorcycle, I am, in the eyes of the law, giving him permission to ride the bike and I am in breach of my contract. So if I have any assets, MCE can take them from me to recover costs.
He couldn't have given the guy permission to ride "his" bike, the bike wasn't his to give permission, the bike wasn't ridden away from the sellers home, it was trailered away, any liability ended with him once the bike was signed over to the new owner.
Any half decent solicitor will get this thrown out within the hour.
Could you imagine stabbing someone to death then telling the police that "the guy at B&Q is an accomplice to murder because he sold me the knife"
It's a laughable nonsense case and the other injured party's insurance trying it on.