Investigation for exposition, Why does the UK not join the Euro?

*The uk prefers not to join because they are then seperated from having the same currency levels as the rest of europe, and by having it this way, they can take advantage of having a better currency, and make a killing off of trading. it's all really a grand scheme, but it works, and no one complains about it, because the currencies are very close, but when you take the marginal revenue of imports and exports, they do make money off of it.