You do not have to have a vehicle to purchase a cherished or private number plate. You can hold a number plate on a retention document or certificate of entitlement for as long as required. The document does need to be renewed each year at a cost of £25 to DVLA Swansea.
You are now able to retain and or transfer a vehicle registration number using the same form which is a V317 DVLA form. These forms can be picked up from your local post office or DVLA office or even most cherished number plate dealers will send you one out in the post if they are doing the transfer of the number plate for you (If the number plate has been purchased off the dealer).