Full information about transferring and retaining number plates can be found
on the gov.uk website:
Retention is the DVLA's way of holding entitlement to a registration number whilst it's not assigned to a vehicle
How to retain a number plate?
Retaining a number plate or transferring it from a vehicle to retention is very straightforward. Using the DVLA Form V778/1.
Complete the form with details of the vehicle from which the number plate will be removed (the donor vehicle) and the details of a nominee.
Only the owner of a vehicle may retain the number plate from it- when the number plate is retained the owner of the vehicle becomes the grantee for the number plate- the Grantee is the only person with rights to the numberplate.
A nominee has no rights to a numberplate and only exists if you as the grantee own a numberplate and want to transfer it to someone else- say a partner or buyer.
When the application is completed you will be asked to send the original tax disc to the DVLA- this is only requested when they have sent you the new tax disc- it is an offence to not display your tax disc.
To retain a number plate costs £105 which is the £25 retention fee and the £80 assignment fee. The DVLA charge the assignment fee up front so when you do come to transfer the plate to a car it's effectively free.
Read more about this in our DVLA fees guide.
You must send your application to DVLA swansea. The turnaround for retention is on average 10 working days but the DVLA officially quote a couple of weeks to cover busier periods.