I am using XE Trade quite frequenty to send money over to the US because the rate they give you is very good and their Wire Transfer Fees are way lower than the banks, I also use it sometimes to do £ to €.
You have to send them the money either via IBAN (if it's €) or if you do £ you can send it CHAPS or BACS and they than send it via Wire (IBAN in €) to your other bank account. There is a wire transfer fee but that is cheaper than the bank's one.
I did £ to € once via CHAPS and the money was on my Irish account on day 4 after sending, they got it on day 3.