Angela its a good move on your part to have kept the original plates as they will go back on.
A few weeks before change over call motability and they will complete the transfer online with the DVLA for you, you just pay the £80 fee, i gave my card details to the motability agent over the phone and he completed the payment.
It can take up to 10 working days to be processed so dont leave it any later than three weeks prior to pick up of your new car.
The only person who got all his work done by Friday was Robinson Crusoe.
Anything i post over three lines long please assume it is an article lol.