When you sell your vehicle later on, you may wish to keep your private number plate. You will need to apply to the DVLA to either transfer the private registration number direct to another vehicle, or retain the number onto a V778 Retention Document. DVLA fees apply.
When the DVLA processes your application, they will provide a standard (age related) registration number to replace your private number plates. This usually the original registration number that was on the car before. But this is not guaranteed.
Allow up to 4 weeks for your application to be processed before transferring ownership of the vehicle the private number plates are on.