I don't think anything will come of this.
If you really had illegal plates them they would give you a fine on the spot and one of those forms where you have to go to the mot station to prove you have changed you're plates and then take it on to the police station. Worst case scenario if they were being really 'funny' they would tell you that you couldn't drive your car with those plates on and you have to change them immediately or leave your car there (this happened to a friend of mine, they actually got put a screw driver and conviscated his plates. Then told h if he drove the car without plates they'd arrest him.)
don't worry about it! If something comes throught the post them cross that bridge when you come to it
Sorry to hear about your S2K!!
Good luck with your search for a decent car.
Post up possibilities on here so we can all give you advise on the best ones!!
im going to all four of mine done this summer. including a colour change. I think the max I want to pay is £200.
I hope I can get this done. but early indications suggest its definitely achievable.