I bought a set of Dubmeister plates a couple of years back. I reckon they set the car off a right (with my ABT Wolfsburg surrounds too). Got loads of Police round where I live and never had a problem with them. In fact, when I was parked up once, PC Plod asked me where I got them from as he wanted some for his Golf too.
According to my MOT-tester mate, the square plates will be perfectly legal providing they have the reflective coating and are stamped with the BS number. There must be somewhere in the internet world that can sort you out!