英国为什么不放弃使用英镑呢

because the uk has a strong currency and does not want to be lumped in with the rest of Europe and their poor economies.

plus, it's already hard within the eurozone itself where ECB has to deal with different economic cycles and different rate of inflation. see what the economies are like within the eurozone..they are the worst hit in this current financial crisis.

it's hard for uk just to give up its currency to join the euro 'cause it's not meeting the critiria anyway.
(http://www.dailyreckoning.co.uk/currency-trading/the-criteria-for-joining-the-euro-in-question.html)