Hi Simon,
I'm doing a similar process. I've never had a new car registered straight to my plate before I always have it registered to its allocated plate and then swap it a couple of weeks later.
Here's what I'm doing / done in preparation for my new GTI
I've put my private plate on my current car onto retention, this is £105 for a 12 month retention. For this you fill out a form and send some documents to the DVLA. 2 weeks later you will get back a letter with the new allocated plate for the car + a tax disc with that plate on and also a certificate which will allow you to get plates made up for that registration. 4 weeks after you receive these you should receive back a new V5C document with the new registration for the vehicle (however I got this the same time as the replacement tax disc). You also receive a retention certificate for your new plate. *Note at this point when you put on the new plates + tax disc you must inform your insurance**
So now I have my current car back on its allocated registration, my private plate is on retention (retention certificate) My new GTI will be registered on whatever plate it is allocated, 13 / 63. Once I have the vehicle I will fill in its plate onto my retention document and send that off to the DVLA, this tells them I want to put my private plate onto that car. (No more payment at this point, the £105 covers taking the plate off 1 car and putting it onto another). So then for my new GTI I should receive a replacement tax disc 2 weeks later with my private plate on. I can then get plates made (if not already) and fit them to my car + my new tax disc. Then inform my insurance of the change.. A new V5C document should also follow a few weeks later.
I find this process easier, as I normally get the dealer to give me the private plate made up for my new car as part of the deal so I don't have to fork out to get those made and it also means in the future when I come to sell the car I already have its original plates made up on physical plates too so again no need to fork out getting them made
