I would not forget exchange houses in London, although not in Paris. The UK still has its own currency and you can therefore still get decent exchange rates with no commission if you know where to go. There are a couple of them with good rates and no commission just outside Victoria Station. Avoid the ones inside the station as they sock it to you on either bad rates, high commissions or both. When I am in London, I use plastic to buy a rail ricket from Gatwick to Victoria Station, then cross the street and exchange money.
Since the euro came in, the exchange houses have worsened the rates and/or commissions in Paris. I would avoid exchange houses there, even though it used to be like London with decent rates being availible back when they used the franc.
There are several things to be careful on in using ATM's. Always use ones attached to a bank. Some of the free standing ones, like at motorway rest stops, add some high fees to each transaction. Also feel the slot where you insert the card for wires slightly protruding. If you find this, go to another ATM, as this indicates someone has inserted a device to capture your card and is probably watching with binoculars from somewhere to get your PIN number.
Another ATM problem that has happened to me twice on Kartnerstrasse in Vienna at different banks and on different trips is that if the ATM in the middle of the transaction loses the signal from your home bank it can flash you a message to this effect and you get no money from the ATM but it is still deducted from your account back home. If you have asked for near your daily limit, it will be 24 hours until you can get more. Fortunately the second time it happened, I realized what was going on and my bank back home was open, so I made an international call and got it straightened out immediately.
The first time, when I didn't know I had been charged, I found out when I got back home and had to go through a lot of crap with the bank to finally get my credit.
