The debit says Visa on it, I've heard if it says Visa, most places will take it, like ATMs anyway.
Don't count on it. I've had some issues with my EC/Mastercard debit card. A few ATMs only recognise the Mastercard symbol and try to treat it like a credit card. Of course this doesn't work.
If I was you I would ask your bank for a Visa credit card specifically for the trip. On most cards you can put some money onto the credit card before you go, this way you can treat it just like a checking account. (It is what I do.)
BTW, the Citibank branch in London is your best bet to get money with your debit card or American Cirrus ATM card. IIRC it is in Oxford street.
[ Edit: Edited on 04-Aug-2009, at 01:55 by t_maia ]
Honestly, I wouldn't exchange any US dollars at Heathrow- the exchange rate is always pretty poor, and instead you can just withdraw money on your debit card as soon as you land from one of the dozens of ATM's there. If your card says visa on it, I'm 99% sure it works in the UK as well despite not being a credit card- I've used an American debit card in Europe and vice versa, and they've always worked like a dream.
To add to this debate, I've successfully used a debit card on the plus and cirrus systems in Europe to withdraw funds from ATMs. It is my understanding that these systems are the most common systems in Europe and that if your card has either (check on the back of the card- or with your bank- it will say) you shouldn't have a problem withdrawing funds from an ATM in Europe. However, I have to admit that I did not use this method in the UK, but guidebooks that I have read do say this, so I think it is still recommendable. Also, debit cards have better exchange rates in Europe than currency exchange places or banks. This includes traveller's cheques.
I strongly recommend that you have at least 5 wallets with the money distributed all over you and your luggage. When you go sightseeing and need to pay for small things use a specially prepared wallet, on that has no more than 20 pounds and small change. Let potential thieves see only this wallet.
Five wallets???? Are you for real? In my travels I have gotten away with having a money clip in my pocket with a few bills in it, a small change purse, and the bulk of my money secure in a money pouch worn around my waiste. Never do I ever let a thief see this (the money belt), or anyone, for that matter, and I do not dig in it to get money as all of the money I need for the day is in the money clip. Also, I wear pants with deep pockets and a material that doesn't show that there are any contents within, not too tight, etc. This has worked for me just fine. Never have I ever been pickpocketed nor, luckily, held up. Also, I keep my wits about me and avoid large crowds where indistinct josteling can occur, stay out of dark alleys, etc. In fact, I do not use even one wallet while travelling. Why such an elaborate ploy?
Also, this website may be of some help, I don't know . . . but I use it to get current exchange rates: www.xe.com/ucc
Good luck on your travels and I hope this helps.