Originally Posted by T8191

Smid ... that experience highlights the benefits of ex-DUB Pre-Clearance and a direct flight from there to the US [wherever]. Doubling back to UK leaves you so vulnerable to those Immigration queues when you eventually hit the US.

When we did it [DUB-LHR-LAX and overnight] we were clearly lucky - our Immigration experience was a painless 10 minutes, after arriving in a BA A380 at 1845 local. However, I'm not inclined to try doing it that way again.