You can take a registration off one vehicle and by retaining it on a certificate meaning it would be ready to be put on another vehicle whenever you are ready to do so.
The certificate is a V778 Retention Document which you can access online.
Previously you could hold a registration for one to three years, but now all new retention certificates are valid for 10 years and are free to renew after that.
Can you retain your registration? – let’s find out:
You must be the person named on the V5 logbook as the Registered Keeper, the registration should be transferable.
The vehicle must have a valid MOT certificate and be taxed.

You can apply online or if you prefer you can use the DVLA form V317, download it, fill it in and send off. If you are applying online you will need the 11 digit DRN (Document Reference Number, found halfway down on the right hand side of the first page).
The registered keeper fills in the sections 2,3 and 9.1, you can pass the rights of the registration number to someone else known as a grantee if you are selling the number, or if you want to retain it for someone else who as yet does not own the vehicle – they are known as a nominee. If you are putting a grantee’s details on the retention form you need to complete 9.1, if you want to put the nominee’s details in you need to fill in the 9.2 part of the form. Please note that the retained registration can be assigned to a vehicle registered in either name only the grantee has the right to the registration. Once you have completed the V317 send it with the V5C logbook (only the original, they do not accept photocopies) to DVLA Personalised Registrations, Swansea SA99 1DS.
However, if the person dies that owns the plate and has left it to you in their will (or you are the executor of the estate), you can keep the number, transfer it to another vehicle, put it in someone else’s name or you can give up the number and apply for a refund. To do any of these things you have to inform the DVLA, as such you will need a certified copy of the death certificate, a certified copy of probate, or a copy of the will or letter from a solicitor confirming who the next of kin is or the executor.
Once you have applied, the DVLA might want to inspect the vehicle -they usually need to check the VIN number and chassis plate, if they want to inspect it the DVLA will inform you. The fee is non refundable if your application is turned down.
When it is approved DVLA will allocate a replacement number, this will reflect the age of
the vehicle. Replacement registration plates are non-transferable, meaning you cannot sell the replacement, but you can replace it with another private registration number when you are ready.
The cost of the retention registration is £80.00 which lasts for £10 years, this includes an assignment fee, this means when you come to assign the registration to another vehicle there will be no further fee. To apply after 10 years to extend the retention certificate this is a free service.
This is not a difficult thing to do, just be methodical, when filling in the forms make sure you have answered honestly and check it before you send it off, (I tend to make a copy so that if you have to answer any questions at a later date you can refer back to the original).
To access the forms that have been mentioned you can go online to: https://www.gov.uk/personalised-vehicle-registration-numbers.