How long is certificate valid for and can you renew it?
DVLA certificates (V750 or V778) are generally valid for ten years. If you haven’t assigned the plate to a vehicle within that time, you can renew the certificates before they expires for another ten-year period. Currently the extension is free of any charge. You can keep doing this indefinitely, so there’s no rush to assign the registration.
Note: You cannot renew expired documents. If the expiry date has passed the document is void and the rights to the registration are lost , permanently. DVLA do not give any exceptions. They do not re-sell expired registrations and nor do they accept payments or offers to re-issue lost registration marks.