We will be traveling from London to Paris next week. What is my best bet to get any leftover pounds changed over to Euros? Also, when coming home should we change our Euros at the airport or wait until we are home and change them at our bank?
Just change your euros to dollars at an airport exchange kiosk before you board the flight. I've never tried to exchange currency at my local bank branch, but if they offered the service, I imagine there would be fees and/or a less-than-ideal rate. Getting rid of them at the airport is more convenient if nothing else. Some people would say hang onto the euros for your next trip, but it would bug me to have fifty bucks worth of currency sitting around that I couldn't use. For pounds to euros, your only option really is an exchange bureau in Paris (or London I guess), such as at the Gare du Nord or the airport. You won't get the interbank rate, but you are paying for a service. The costs of exchange are insignificant compared to the overall costs of a European trip.
We usually exchange at Wells Fargo before we go, in your case buy Euros and Pounds. Their rates are OK and they will buy back leftover bills. If you add up the fees from using ATM's and exchange kiosks it's a good deal.
We brought home around £20 and change, and around €8 in change from our trip last weekend. We'll just keep it until we return. Changing money is a good way to lose money. We get our cash from an ATM machine, not from a money exchange. And following Rick Steves advice, we brought a few hundred in US Dollars as an emergency backup. Never needed it, the ATM machines all worked (ING in Amsterdam, and Barclay's in London).
To actually answer your question changing pounds to euro will have to be done at an exchange bureau. Exchange rates and fees will be a little high and you do a little better if you waited until in Paris but then you have to find a place. I doubt if you local bank will exchange currency. American express will and again you will lose upwards to 10% on the exchange. Another option is to sell to another traveler. When we return we try have between 100 and 200E for the next trip. Recently has been a better investment than the stock market. Sometimes if we return with too much will just try to sell locally via this site or other travel sites. Sell them at the interbank rate and it is a good deal for both parties.
"Some people would say hang onto the euros for your next trip, but it would bug me to have fifty bucks worth of currency sitting around that I couldn't use." In 2000 I brought back €200 that cost me 89¢/Euro. Now the Euro I have at home would cost $1.37 ea. I've made almost $100 off the inverstment.
Double exchanges. Which what you are planning on doing are not great. E.g. change dollars into pounds, then pounds into Euros then Euros back into dollars. So I would keep the amount very small. One option is to bring it home and keep them for you next trip. I am guessing you have already dismissed that. I don't know if your home bank or still in Europe will give you a better rate. But in London they will take your British coins, in Paris they won't. At the Paris airport they will take your euro coins your bank at home won't. So if you are talking about $30 dollars worth with even if only a dollar or two is in loose change, the change will offset any difference in exchange rates. If you are absolutely certain you are never going back, another option rather than your bank would be a friend, family or coworker you know are heading over there and exchange the money at the official rate, with neither of you taking a hit on the banks profit. Plus they will appreciate the coins (which the bank won't take), when they hit the vending machine for a soda or the pay toilets to get rid of surplus soda.