money conversion

Don't convert - withdraw.

And ALWAYS Say No To DCC (dynamic currency conversion - would you like that in pounds or your home currency so you don't have to worry ).

I've heard of people arriving in Rome when the ATM "fillers" were on strike and all the ATMs were empty. Once I tried to get cash from an ATM (not at an airport) when the computer lines were down and the ATMs didn't work. Also, I once arrived at FRA with three ATM cards, and when I tried to use them, the first two just resulted in a "call your bank" message. The third one worked, but it was still comforting to know I had 200€ in my pocket and didn't need the money from an ATM right then.

Today, Wells Fargo is selling 150 GB Pounds for $207 (about 5% over the Interbank rate of $197 for 150£). Depending on your bank, you would pay $197 to $205 for the same 150 Pounds at a bank ATM over there. That's $2 - $10 to know you have cash when you get there. I think that's cheap insurance. It's not the probability of not getting cash from the ATM, it's the consequences.

How many people would take all of their dollars out of their wallets before flying cross-country, "knowing" that they could get cash from the ATM when they landed?

Lee made a very good point about the relatively low cost to have local currency in hand when you land. $10 or even $15 is very little compared to the overall cost of the trip. As is the case with all insurance, better to have it and not need it than the other way around.

We always go with at least hundred or so of the local currency. Just to gets through the airport, maybe a taxi to hotel, etc. and then hit a local bank's ATM for more local currency. We either save the hundred or so from a previous trip or get it at our local bank paying a fee of 5 to 10% fee. After that, the debit card and a bank owned ATM in country is the cheapest and most convenient way to obtain local currency. Take two debit cards tied to two different accounts just in case one goes bad. Has never happen to us but there is always the first time. Careful with Heathrow, some reports say all of the ATMs are now owned by a currency exchange bureau with questionable exchange rate. Will be there in three weeks so will see if that is true.

As has been reported on here (see the bottom of this thread), the ATMs at Heathrow may not even these days try to trick the unwary into DCC, let alone have other fees.