Say for example the number plate on a car is CN05 FLU. I then put a private plate on the vehicle. When I sell the car in the future, does the vehicle revert to CN05 FLU or do the DVLA assign a new number altogether?
I think you'll find that once a registration number has been assigned it stays what it was when new. You make application to DVLA to change the number, if you then want to sell the car and keep the new plates you reserve them to yourself and the car reverts to its original number. However if you request a new car with your plates on them and you reserve the plates, then a new number is issued at sale. I'm going back a few years but that's how it used to work