Once upon a time everyone knew who was No. 1. My mates, my Mum and probably your Mum too - knew if Blur had beaten Oasis, and whether the Spice Girls had managed to get their sixth chart topper in a row. Now that's no longer the case. Unless it's the Christmas No. 1, with its attendant media hoopla, the specifics of who exactly is heading the charts often passes us by.