It was a Fidelity Cash Management Account Visa debit card, so it's a similar but different data point. Now, I didn't actually try to draw Euros from the ATM, only GBP, so I don't know if the ATM would have tried some multi currency conversion obfuscation with EUR or have used the Visa rate as well.

My last trip was on the day of the BA IT meltdown, so I was running from T5 to catch another flight from T3. I didn't have time to test some corner cases like known DCC establishments with Android Pay. I was getting some GBP for my parents.

I also used a Travelex ATM landside in T5 without DCC in May 2016 and didn't experience DCC. In fact, the only DCC I encountered was at Grosvenor House and the LHR Marriott, and both places offered an easy, no pressure opt out.

My memory is a bit fuzzy, but I believe DCC was offered during my November 2011 trip at a Travelex ATM in T3.