Try Citibank.co.uk. I opened a USD account with Citi this summer.
Their london branches are open until 8pm and the online service is reasonable, you can swap from USD/GBP/EUR immediately with a much smaller spread on the exchange rate than using a bureau de change or using most credit cards abroad.
Another feature I like is that if you have multiple current or savings accounts in different currencies, you can phone up whenever you like and they'll immediately change the link on your debit card so it charges whatever account you want to use.
Their current accounts pay a derisory rate but the savings accounts are better than the 0.9% you are talking about. Also, there is a monthly charge for foreign currency current accounts if you don't keep GBP2k equivalent across your whole relationship with them, however they don't levy this charge on savings accounts so you could just have a usd saving account for free.
Hope this helps