Obviously a front is a must in the UK. If there are mounting points for a plate there's no excuse for a plate not to be there even if its just taped on its sufficient.

My mate had a new bumper put on his saxo a couple of years ago, went to lakeside and got 3 points and £60 fine for not displaying a number plate even though it was in the front window. He hadn't got round to drilling the holes as we were busy with finishing our college work, ended up going to the services and buying some duct tape to put it back on.