It's now incredibly easy on-line. Take off - https://www.gov.uk/keep-registration-number You pay £80 and it's valid for 10 years - once the online application is successful, you can use the retention certificate which will be issued by post to assign the personalised registration to a new vehicle. Again it can be done on-line. Put on - https://www.personalisedvehicleregistration.service.gov.uk/assign/vehicle-lookup But beware - this is the new 'Beta' service which only works Monday to Saturday 08:00 to 18:00. At other times those links will say 'Service Unavailable' or 'Page cannot be found'.