Full information about transferring and retaining number plates can be found
on the gov.uk website:
Retaining number plate and retention refer to holding entitlement to a number plate whilst it's not assigned to a car.
A registration number can be held on retention for up to 12 months- but then must be renewed.
If you have a number plate on a vehicle and you wish to retain it then you can only do so if you are the registered keeper of the vehicle.
If you are not the official registered keeper of a vehicle then you simply have no right to retain the numberplate.
If your V5c registration document (logbook) states that your registration number is non-transferrable then you are unable to take part in the retention scheme.
Refer to our how do I retain my number plate section for greater detail but retaining a number plate costs £105 at the time of writing.
On average 10 working days but officially the DVLA can take a couple of weeks to successfully complete a retention application.
To retain a number plate you will require from V778/1 - Retention of a vehicle registration number.