For a UK (or other currency) draw from a US account, this tends to be the best way . . .

For a foreign currency draw from a UK account, it actually depends. UK accounts are notorious for charging a 5 GBP fee on foreign withdrawals, so depending on how much you're taking out, the fee can be more expensive then the rediculous spreads that the cash conversion windows charge. That being said, if you're taking out $500, the ATM is probably the way to go, but for smaller denominations, you might want to think about other alternatives.