Manchester United are England's biggest club, for a whole variety of reasons but they always have been. Even in the 70s they were drawing huge crowds, the biggest. They have a pull beyond any other, the Munich disaster pulled the whole country behind them and there is an undeniable romance about them. Liverpool, are the only English club in the same stratosphere as them though, the only club who deserves the title as 'one of the biggest clubs in the world' in England.
Liverpool have gone 30 years without a league title, yet they still generate more press attention than Arsenal, Man City, Chelsea...they're just a significantly bigger club. Liverpol have always been a step behind the modern game though, but now they look they're rectifying things a little bit.