I'm trying to remember how it worked at Heathrow then, as I wasn't (to my recollection - another jet lagged passenger here!) following signs stating that I was a domestic passenger. I got off my international flight, followed signs for T2 connections and ended up at a border check point. I'm not sure how anyone would have differentiated me (as someone entering the UK) from people transiting to elsewhere. I had assumed (evidently incorrectly) that all passengers transiting had a quick passport check, even if they were transiting to elsewhere (which I had imagined being a quick "wave through").
--- old post above --- --- new post below ---
I don't want to claim that anyone was incompetent, but the border guard literally looked at the passport for a couple of seconds and waved me through. This is very different from entry to the UK, where (unless I'm using the e-gates) I do frequently get asked questions about my trip. Perhaps I just look suspicious?
There was no concern as to where I had been (it is worth considering that Etihad and Emirates fly into the airport and offer connections, so it isn't all US traffic) or where I was going to. Customs at Edinburgh was non-existent - for those who don't know Edinburgh airport, customs consists of a blue lane and a green lane. There was also a closed kiosk and phone for passengers who had something to declare. I noted that, coming off my flight, quite a lot of people had orginated in the US (or elsewhere outside the EU, as noted by the absence of green stripes on the baggage tags) but erroneously took the blue channel. Not that there was anyone to stop them.
I'd suggest (although I'm not advertising it to would-be criminals!) that the border checks on that occasion were very lax and could be strengthened.