Why does Manchester (UK) rub up London so much?

See politicians are grumbling about the construction of the super-casino in the northern city, using the words 'criminal activities' to dismiss whatever progression may ensue. They were not so keen to mention that when the Millennium Dome was up for it, or for that matter, Blackpool (the natural place for it, surely). In 2002, Commonwealth Games in Manchester had the London based press sneer and snarl, and I suspect they'll have all the reason to continue as the finances are becoming a circus for the 2012 Olympics. I'm not a great lover of either city, but living half-way between them gives a sharper mind on how petty and envy-ridden England actually is.