For the last 15 years I have probably gone into LHR or LGW, 90% of it being LHR, a total of nearly 100 times. Actually, maybe more like 120 times. I have never had a negative experience with customs and immigration. A couple times they werent paying much attention, but more frequently they have been overtly polite and friendly in welcoming me to the country. And a lot of these are weird itins, arrive Saturday, back to NY on Sunday for MRs. I recently signed up for the Iris program but that was just to avoid the lines.

I should add that why I can sign up for something like the Iris program in the UK, but not in the US when I am a US citizen boggles my mind.