Your question isn’t very clear and your subject certainly isn’t – I thought you were asking for work opportunities in banking. If my answer is not suffucuent and you need to re-ask, be clear in your question heading.

I’m not sure what you’re actually asking so I’m going to guess. I’m also assuming (also not clear) that you are an American and will be studying in London.

If you have money in your American Bank account and withdraw funds from an ATM in the UK, you will get charged. Most Banks do this. The conversion rate from GBP to USD is likely to be reasonably favourable (although it may not feel like it, given the state of the dollar right now) and they will generally deduct a small percentage on top as a cash handling fee. The conversion rate will generally be better than you will be offered if you were to try to change physical cash.

You might want to talk to Citibank – they have a few retail branches in the UK – or try HSBC if they have a branch near to where you currently live and see if they can suggest anything. Note that most American Banks do not have retail branches here in the UK, so you cannot just go in and go to a cashier….they have international branches that deal with big multinational corporations, but not the person on the street.