Why keeping it updated matters
The V5C registration certificate, often called the logbook, records who the DVLA has as the registered keeper of a vehicle. The registered keeper is not necessarily the legal owner, but it is the person the DVLA and the police will write to about the car, including tax reminders, MOT correspondence and, if something goes wrong, fixed penalty notices.
If a car is bought, sold, or its keeper's address changes, and the V5C is not updated promptly, correspondence can end up with the wrong person. A previous keeper can receive penalty notices for a car they no longer have, while the current keeper might miss letters that matter. Keeping the record accurate matters for both sides of a transaction, and updating it with the DVLA costs nothing.
How to update your V5C
Updating the V5C is straightforward. When a car is bought or sold, both parties complete the relevant section of the V5C and post it to the DVLA, or update the keeper online using the reference number and the 11-digit document number printed on the certificate. A new V5C usually arrives within a few weeks.
Moving house is simpler still: the address can be updated online without changing the registered keeper. Anyone selling privately should keep the yellow "new keeper" slip, since it is evidence the DVLA was notified of the sale. It is not, on its own, proof of the sale itself — that comes from a separate receipt.
Before buying a used car, it's worth checking that the V5C paperwork matches the vehicle in front of you: the VIN, the registration and the keeper details should all line up.
A mismatch between the V5C and the car, or a seller who cannot produce a V5C at all, is a reason to check further before handing over any money.