If the scale and polish doesn't shift it, then you could always try one of those teeth whitening products you can get from Boots and various places. I seem to remember a lot of people on here raving about one particular product but unfortunately I can't remember the name of it and the Boots website is down.
Edit: A quick search tells me it may have been Crest Whitestrips, but apparently you can't get it here in the UK.