You may have a point there. In fact I'm gonna get in touch now and let them know I'm cool to do the transfer after collection. Thanks 2014GTi 
Yes, have a word with them and see if they can do the transfer after collecting, if your part exchanging a car then this might provide difficult.
So in future folks, if you have a private plate on your car, have it removed a month in advance and ensure you have the retention certificate to hand.
During busy periods like March / Sept 1st or Xmas DVLA can take ages dealing with registration requests.. the best advice would be to have your car bought on the original plate and then sort out your own private plate afterwards.
The plus side is that you have the original set of plates to put back on when you come to sell it
