I've just learned that our car transfer company does not accept credit cards, so I will need to have cash. Only other time we attempted to use ATM out of the U.S. we ran into trouble (in the Caribbean). Yet I assume that changing $$ into BP here in the States is a waste of money. So: Is it simple to use the ATM's in Heathrow? Where are they exactly? Any other special advice to make the transaction comfortable much appreciated.

There are plenty of ATMs outside customs - precise location depends on your terminal and which bank preferences you have. No problem with US cards working. Note some US banks have agreements with UK banks (e.g. BofA < > Barclay's) where transaction fees are waived.

Have enough cash reserves that you could change to pounds in a pinch.

Sometimes the US banks are unable to verify for an hour or two. Usually in the middle of the night in the US, which may be when you will be arriving.

On one trip to Londonh, the first 4 times I tried the ATMs, my debit card was declined. I had lunch, and it worked fine in one of the same machines an hour later.

Keith

I would find a company that accepts credit cards.

In the very very unlikely event that you are unable to get pounds in Heathrow, your driver can stop at an ATM near your destination.

I agree with blightyboy.

Would I, woozie after an overnight flight and struggling with immigration, get into an unmarked car with a stranger who will only accept cash?

I don't think so.

There are alot of drivers that only accept cash - can't quite figure out why - but the ATMs are all down near where you come in - if you come in the right side of the airport, head left. I've used my ATM card all over the world, and definitely never had problems in Heathrow.... last time I was there, my driver only accepted cash, and he held my luggage until I brought it back....

I always use justairports.com & they're much cheaper if you pay in cash. If you can't find an ATM, just change enough at an exchange bureau.

Even with a rotten exchange rate they'll charge you, it's at least an option.

They take cash only as it is a way of them avoiding paying tax and this will save them approx 20%.

I so much appreciate the many folks who took the time to respond: so many helpful suggestions, plus it was interesting to read the variety of opinions.

Gardyloo: glad you mentioned the B of A tie-in with Barclay. I never use my B of A card here, but that's the one I'll be sure to take on this trip. thanks.
Keith: Good idea to take extra $$ in case cards don't work. I think I'll get a couple of hundred in traveler's checks.
blightyboy and Ackislander: I have no concerns about the company. They're highly regarded, I've been in close touch with them, and I won't feel at all as if I'm entering an unmarked stranger's car.
kayd: yes! I clapped my head and said, of course-- why didn't I think of that?! thanks!
debi/carrybean: thanks for your in-put!

Thanks, everyone: I definitely feel 100% more easy about all this now.