I have used the ATM machines at Heathrow Terminal 5 during all but my last trip. There were several of them located in the baggage claim hall. Last year, we changed planes at Heathrow and flew on to Paris, so we didn't go through the baggage claim at all. While waiting in the main concourse, I noticed that there were no ATMs. If you needed cash, either with your ATM card or by changing dollars to pounds, you had to go to one of the commercial money-changers, and pay a hefty fee.
Are the ATMs in the baggage claim hall still there? Or has the London Airports Authority figured out a way to stick it to us?