It's politics and self-image. Although the mid-level business community is for joining, the angry Daily Mail proles aren't, and the feckless rich aren't. With the Tories practically guaranteed a win in 2010, there's no pressure at all to join - they're certainly not going to propose it because their base would skin them alive.
It's more important to most of the population to cultivate a narcissistic image of specialness than it is to deal with reality. So we're going to sail through 1:1, it's going to be the ECB's fault because of something or other, and we're going to carry on down to the floor - wherever that is.