I've just sold my car to a buyer in South London but I'm uncertain as to when my liabilities will transfer to the new keeper. I prepared a handwritten receipt, which both buyer and seller signed at the time of transfer.

The car is being driven to its new keeper address untaxed. The buyer says his insurance will cover him to drive it but it will inevitably be spotted on some ANPR device in London. It may even commit a parking offence. What precautions can I take to avert liability?