Maybe now would be the time to invest in a cheap set of private plates?
As you are inevitably going to be pulled up with some frequency over the next few weeks, I would keep some form of proof of ownership of the vehicle with you to make things nice and simple.
"Do you know why we have pulled you over?"
"Yes officer, I reported my registration plates stolen, here is my licence, insurance docs and V5 to prove I own the car."