Learn to Economics.
Thwe only reason the Dollar works in such a vast country like America is that you're all one economy, in effect - Britain has a vastly different economy to the rest of Europe for a variety of reasons - one of the largest being that we're buyfags whilst they're rentfags.
Also, the countries in on it now have different economies to each other - Germany reckons it can handle the strong exchange rate, but France and Italy are getting pissy about it and want to devalue the Euro. Tensions are rising and when and if the shit hits the fan, Britain won't be a part of it. Obviously we'll be affected, the whole world will in some way or another, but not by nearly as much as we would be if we had the Euro.