Live Departures from London Heathrow Airport (LHR), London

London Heathrow is the UK's largest airport and one of the busiest in the world, handling tens of millions of passengers a year. It sits about 25 kilometres west of central London and works as a full international hub: long-haul flights connect onward through it as much as they start or end there, which is why the terminals stay busy from the first wave of arrivals before dawn.

Heathrow runs on two runways near capacity and four passenger terminals (2, 3, 4 and 5 — Terminal 1 closed in 2015). It serves more international destinations than any other UK airport. Expect scale rather than calm: this is a working global hub, not a quiet regional field, and it sits at or near the top of Europe's passenger tables.

British Airways is the dominant carrier and the reason Terminal 5 exists, flying the widest long-haul network from Heathrow alongside short-haul European routes. Virgin Atlantic bases its operation here too, mostly transatlantic and a few long-haul leisure routes. Between them they account for a large share of the departure board, with the rest of the world's major airlines filling in: the European flag carriers such as Lufthansa and Air France on short-haul, and the Gulf and Asian long-haul carriers — among them Emirates, Qatar Airways, Singapore Airlines and Cathay Pacific — running their flagship widebodies in and out through the day.

The network character is long-haul international first, short-haul European second. There is very little domestic flying compared with regional UK airports, and almost no turboprop work. What you see instead is a steady rotation of widebodies — the 777, 787, A350 and A380 families — to North America, the Gulf, Asia and Africa, which is what makes Heathrow a place where seat choice on a long flight actually matters.

Heathrow's four terminals are spread out, so check which one your airline uses before you travel — British Airways and Iberia sit in Terminal 5, Virgin Atlantic in Terminal 3, the Star Alliance carriers in Terminal 2, and the SkyTeam carriers in Terminal 4. The terminals are linked airside and by free inter-terminal transfer, but they are not a short walk apart. Getting there is straightforward: the Elizabeth line and the slower Piccadilly line both run on the Underground network into central London, the faster Heathrow Express runs non-stop to Paddington, and the M4 and M25 reach the airport by road with short-stay and long-stay car parks at each terminal.

The departure experience is what you'd expect of a major hub: large check-in halls, busy security that moves faster at off-peak hours, and a long airside walk to some gates, so leave time. Lounges are extensive here — British Airways, Virgin Atlantic and the international carriers run their own, and there are paid lounges open to anyone with the right ticket or membership. Give yourself longer than you think for a long-haul departure, particularly through Terminal 5 at peak.