Trekker, best of luck! This is what I noted in a trip report in June about arriving in Heathrow Terminal 3. Not everyone will agree, I feel sure, and hey, I'd been on planes for 30 hours or whatever at that stage:

A well known travel writer once said: “When I die, and if The Lord sends me to Hell, I just beg he does not make me go via Terminal 3 on the way out”. Experiencing this lunatic asylum first hand makes that comment really mean something. The place is like Dante’s Inferno. Miles of needless walking, chaos everywhere, and delays. “Terminal 3” (of the 4) is used mainly by long haul USA and International carriers - but not Qantas or BA of course, who use the newer #1 and #4. The arrivals section is like a Russian Zoo.

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~ Glen ~